Editor’s note: This is an updated version of an article published in 2018, 2019, and 2020.

Opinion post by
Robert Triggs

USB-C is billed as the solution for all our future cable needs, unifying power, and data delivery with display and audio connectivity. Ushering in an age of the one-size-fits-all cable. Despite the USB-C connector supplied as default in modern smartphones, the standard has, unfortunately, failed to live up to its promises.

Read next: What are the best USB-C headphones?

Even the seemingly most basic function of USB-C — powering devices — continues to be a mess of compatibility issues, conflicting proprietary standards, and a general lack of consumer information to guide purchasing decisions. The data speeds available over USB-C have also become increasingly convoluted. The problem is that the features supported by different USB-C devices aren’t always clear, yet the defining principle of the USB-C standard makes consumers think everything should just work.

What’s changed over the past four years?

We’re now into our fourth yearly update of this article so let’s take a quick look back at how things have changed and even improved somewhat during that time. Particularly in the past twelve months.

USB Power Delivery (PD) has become an almost universal charging standard in both the smartphone and laptop markets. Even phones that rely on proprietary fast charging technology have mostly embraced the technology. Meaning you can now charge most gadgets somewhat quickly with USB-C to USB-C plugs and cables. Unfortunately, as we’ll see throughout the article, USB-C charging implementations are still often far from comprehendible for most consumers. Particularly with the addition of USB PD PSS.

In the laptop space, USB-C ports are increasingly more numerous than older USB-A sockets. Although the capabilities (such as charging, display, and audio) of these UBS-C ports still vary widely from laptop to laptop. Overall things are better, but USB-C remains a bit of a mess.

Still a consistent example of USB-C compatibility problems: Charging speed

Samsung Galaxy 21 prefered power input

Credit: Robert Triggs / Android Authority

There is a very common frustration with the USB-C standard in its current form. Moving phones between different chargers, even of the same current and voltage ratings, often won’t produce the same charging speeds. Furthermore, picking a third-party USB-C cable to replace the often all too short in-box cable can result in losing fast charging capabilities. As can opting for a third-party USB-C power adapter that supports Qualcomm’s Quick Charge or USB Power Delivery rather than one of the numerous proprietary standards.

We’ve tested this numerous times in the past and found that USB-C phones from popular brands, including Samsung, Huawei, LG, Google, and OnePlus, all slow down their charging speeds once you begin to mix and match cables and chargers. Using your old charger with a new phone can be a problem. An issue that’s exacerbated by Apple’s iPhone 12 and Samsung’s Galaxy S21 series which don’t ship with boxed chargers.

More about USB-C: How fast charging really works

The graph below showcases how mixing and matching cables and chargers drastically reduces USB charging speeds compared to the cable and charger provided in the box. The take-away is that charging speeds over USB-C vary widely from handset to handset.

Although major compatibility issues are increasingly limited to older USB-A to USB-C connections that use on older or proprietary standards. For the most part, USB-C smartphones plugged into USB-C Power Delivery plugs offer somewhat faster than basic charging speeds. Although this still isn’t guaranteed.

For example, 2021’s Oppo Find X3 Pro refuses to fast charge with anything except Oppo’s SuperVooc chargers. But this is uncommon. Even though most phones work correctly, figuring out exactly what speeds you’ll obtain remains virtually impossible to tell at a glance.

Complicating the matter is the adoption of the USB Power Delivery Programmable Power Supply (USB PD PPS) standard. Samsung was the first major brand to adopt this standard and it’s the only way to charge the Samsung Galaxy S21 series at its 25W maximum speed. While the standard is backward compatible with USB Power Delivery, the graph below shows that USB PD chargers provide inferior speeds.

USB PD PSS is a key step for universal fast charging, as its flexible charging voltage is important for maximizing battery charging efficiency. But it’s come at just the wrong time and undermines what little cohesiveness has developed in the charging ecosystem these fast few years. Ultimately the subtle difference between USB PD and USB PD PSS is yet another headache for consumers.

USB PD PSS adds another layer of confusion to consumer purchasing decisions.

Overall, the industry has been moving in the right direction. USB Power Delivery is gradually solving the fragmentation issue, although proprietary standards remain commonplace in the smartphone market. Particularly where Chinese brands are concerned. Confusion regarding the PPS variant should subside as industry support improves in the coming months and years. But overall, charging is still a bit of a mess.

USB Power Delivery – the broader picture

Belkin Boost Charge Dual USB C PD GaN ports

Credit: Robert Triggs / Android Authority

USB Power Delivery has become the de facto mobile charging standard, with compatibility also extended into the latest version of Qualcomm’s Quick Charge. Even though proprietary fast-charging standards are still very common, third-party accessories are now predominantly sporting USB Power Delivery specifications. This is helping to make accessories easier to buy.

The drawback, however, is that it is still far from clear exactly what charging speeds you’ll obtain from any charger or handset. See the Samsung Galaxy S21 accessory test results above as the perfect example.

Read more: This is the best Samsung Galaxy S21 charger you can buy

USB PD PSS can hit 25W and even 45W on supported devices, but plugging the same phone into a USB Power Delivery plug sees speeds hover around 15W typical. Likewise, Quick Charge 3.0 devices often fall between 9 and 18W. But worse still is that capabilities with other standards are seldom clearly listed by manufacturers, so there’s no telling what to really expect from any given plug or accessory.

Support for Quick Charge has wained, but USB Power Delivery now widely supports fast(ish) charging.

If you’re looking for an example of charging done right, the OnePlus 9 series is an excellent example. Despite supporting 65W proprietary fast charging, the phone will still charge quite quickly by drawing 25W from USB Power Delivery plugs. Likewise, OnePlus’ Warp Charge 65T charger supports USB Power Delivery and its Programmable Power Supply variant and can supply up to 45W of power to compatible laptops and other smartphones. It’s a very good charger for all your other USB-C devices and other brands should aim to emulate this setup.

Related: The best USB-C cables you can buy

Ultimately there’s still very little consistency about the charging speed of smartphones and no easy way for consumers to know if, or how well a handset will charge using any given plug. This becomes even less clear when products start using bi-directional charging capabilities, such as charging your phone from your laptop’s USB port.

More than just charging: USB-C speed for data

USB-C connector close up macro shot

Charging is still overly complicated then, and it’s the same situation with data transfer speeds. USB-C supports 2.x, 3.x, and Thunderbolt speeds for some ports, which is confusing enough. However, cables also have to be specifically rated to meet higher speed requirements.

The introduction of USB 3.2 and its ridiculous Gen 1, Gen 2, and Gen2x2 branding threw up another hurdle for those trying to get their head around the increasingly complicated naming scheme. Just days later, the USB 4 announcement drained any remaining comprehension from consumers and developers alike. USB 4 claims to “minimize end-user confusion”, as it mandates a USB-C connector and USB PD support, but it still offers a confusing array of optional features, such as Thunderbolt 3 on just some devices. Ultimately not all future USB-C ports will be USB 4, so it’s unlikely to solve the problem.

There's no way to tell if a USB-C cable supports high current charging or 4.0 data speeds just by looking at it.

The USB data naming scheme is undoubtedly a mess. The table below will hopefully help to sort out what each specification offers you.

GenerationSpecificationOptional Consumer BrandingDataspeed
USB 1.xUSB 1.0Full Speed USB12 Mbps
USB 1.0Low Speed USB1.5 Mbps
USB 1.1Full Speed USB12 Mbps
USB 2.xUSB 2.0High-Speed USB480 Mbps
USB 3.xUSB 3.0SuperSpeed USB5 Gbps
USB 3.1Superspeed USB+10 Gbps
USB 3.2USB 3.2 Gen 1SuperSpeed USB 5Gbps5 Gbps
USB 3.2 Gen 2SuperSpeed USB 10Gbps10 Gbps
USB 3.2 Gen 2 2x2SuperSpeed USB 20Gbps20 Gbps
USB 4USB 4.040 Gbps (Thunderbolt 3)

Devices and cables are just as problematic when it comes to supporting “Alternate Modes” and other protocols. These fall under the USB-C specification rather than the port’s data speed specification. These include DisplayPort, MHL, HDMI, Ethernet, and audio functionality provided over the connector, all of which rely on the connected devices and cables to support them. These are not a compulsory part of the port specification, as capabilities and needs clearly vary from device to device. USB 4, for example, introduces DisplayPort 4.1a and PCI Express data support, but you don’t need that on a battery pack.

The problem with this is that certain functionality that a user might expect in a product isn’t necessarily provided. Consumers may assume HDMI or Ethernet are supported over a USB-C port if a laptop is missing the regular ports, but that might not be the case. Even more frustratingly, functionality might only be restricted to specific Type-C ports on the device. You might have 3 ports but only one that offers the functions you want.

USB-C is compatible with lots of features, but not every port supports everything. USB 4 does too little too late to help.

USB-C makes functionality more opaque, not less. It claims to do everything, yet there’s still no guarantee a product will actually work with any of these features. USB 4 may help unify some feature compatibility, but I doubt it will help end confusion while USB-C 3.1 and older ports still exist. The sheer range of legacy devices and remaining optional standards means that USB-C port capabilities remain unknown at a glance. Even when more detailed information is available and ports are correctly marked with the appropriate branding, making heads and tails of the various modes and jargon can be a lot of information for someone to digest when all they want is something that works.

Tested: The Google Pixel series has a strange USB-C transfer problem

Port shortages are less of a problem

USB C port Samsung Galaxy S Book

This brings us nicely to the biggest problem with the reversible USB port, at least with smartphones: there’s a lack of them on devices. A single port for audio and power is already proving problematic in the handset space, with consumers reaching for dongles and hubs to fix the issue at their inconvenience. Although the swift move to Bluetooth audio is making this less of an issue for some consumers.

Even so, this opens up a whole new world of compatibility problems, such as whether your hub or dongle supports the same charging method or standard for bi-directional power, or if data can still pass through to another device.

Trial and error is often the only way to figure out what a USB-C port supports.

Fortunately, the latest laptops on the market are now including more than one USB-C port. Higher-end laptops also increasingly support display, audio, and other features over their USB-C ports. Although this isn’t necessarily a given. Implementing these advanced features isn’t cheap and so laptops often only sport a couple of advanced USB-C ports, meaning that the dongle-life is still a problem for users who use lots of accessories.

It’s taken a few years but laptops are finally embracing USB-C not just for power but for the variety of other features that the port supports. At least in the high-end market, USB-C is starting to live up to the initial promise.

Why the compatibility issues?

Purple USB A to USB C cable

Cable compatibility, arguably the most frustrating of USB-C’s problems, stems from legacy support for slower devices and the introduction of higher-speed use cases like video data. USB 2.0 features just four-pin connectors for data and power, while 3.0 cables increase this to eight. So USB-C to A cables, which are commonly used for charging, can come in 2.0, 3.0, and 3.1 varieties, which affects the amount of data and power they can handle. USB Power Delivery is backward compatible and so is the best option for charging up devices using older cable types and speeds, but the prevalence of proprietary standards means consumers rarely really know what they are getting.

Cable quality, rating, and length affect the features available over a USB-C port. Some cables even breach the standard!

Cable quality also comes into play here, as some charging standards will detect how much power a cable can handle and set the appropriate charging speed. In our earlier example, Huawei’s technology requires a 5A rating to charge at full speed but this breaks the specification and so the cable doesn’t work with Google’s Pixel phones. This is why longer cables from third parties won’t always offer the same speeds as the smaller ones included with your phone.

If that wasn’t complicated enough, the introduction of high-speed data and real-time video transfer has introduced new problems. Very fast signals suffer from attenuation and clock jitter when transferred over long distances, meaning data can get lost along the way. To address this issue cables can also come in passive or active varieties. Active cables include re-drivers to restore the signal amplitude and prevent a loss in signal quality over long distances. So long cables used for very high data speeds (such as sending 4K 60fps video or data over Thunderbolt) require active components in them, while basic charging and data transfers can get away with a standard passive cable that’s less than two meters long.

DisplayPort, MHL, HMDI, and Thunderbolt are supported via passive USB Type-C cables at less than two meters if they carry the “trident” SuperSpeed USB logo or less than one meter for SuperSpeed+ labeled cables. Active cables will be required for further distances and you’ll have to look out for the Thunderbolt logo if you want 40Gbps speeds. Passive adapter cables to other USB types won’t support any of these modes.

USB Type-C Alternate Mode cable support

This table shows which Alternate Mode protocols are supported by which cable types.

Feature compatibility issues also involve the port and device in question, which can be configured for a wide selection of charging speeds, legacy standards, and alternate modes. USB-C is a more complex port than its predecessors, requiring substantially more software and hardware input to get things working correctly.

The starting point for USB-C products is the Power Delivery protocol. This isn’t just about charging, it’s also how the port communicates support for extra features like HDMI and DisplayPort by using the connector’s additional pins. All of the Alternate Modes use the Power Delivery Structured Vendor Defined Message (VDM) to discover, configure, enter, or exit these modes. The bottom line is that if your device doesn’t support Power Delivery, it won’t support any of these other features either. Unfortunately, Power Delivery circuitry is more complicated and expensive than the barebones circuity, and the complexity scales up with the number of ports.

USB-C audio is basically dead as Bluetooth takes over.

Even so, this doesn’t mean every Power Delivery port or device will support every feature. It’s up to device manufacturers to include the necessary multiplexers and other ICs alongside the Power Delivery components and regular port connections to support Ethernet, display, and other Alternate Modes. The diagram below shows just some of the different component blocks required to scale up the feature set of just a single USB-C port.

TI usb type-c port components

Just one of the many possible configurations to support some advanced USB Type-C features.

The port circuitry only becomes more complicated when products want to route and manage multiple signals, such as video or audio, to multiple USB ports. The signal routing becomes increasingly complex and expensive so manufacturers restrict functionality to only one or two ports

Even delivering power requires a complicated circuit with USB-C, in order to accommodate for the reversible connector type, the range of power options, and the choice between upward, downward, and bi-directional charging port and data options. To cut down on costs and complexity, not all USB-C ports on a laptop or PC sport everything. USB 4 aims to help by mandating a few features, but that seems unlikely to help if devices mix and match new and old standards to save on costs and complexity.

USB-C will remain a mess

OnePlus 8 Pro vs Samsung Galaxy S20 Plus USB C

USB-C’s complexity has undoubtedly been its undoing. Although the idea of one cable to support everything sounds very useful, the reality has quickly become a convoluted combination of proprietary versus on-spec products, differing cable qualities and capabilities, and opaque feature support. The result is a standard that looks simple to use but quickly leads to consumer frustration as there is no clear indication as to why certain cables and features don’t work across devices.

Fortunately, high-end laptops are increasingly embracing the full potential of the USB-C specification. Smartphones have by and large embraced a shared charging standard, but the situation is still far from being straightforward in most instances.

Not all USB-C ports or cables are equal. Despite efforts to unify, USB 4 can't fix the compatibility problem.

USB 4 is a mixed attempt to unify the USB-C port, and it certainly can’t solve the problem on its own. Better labeling could help consumers identify which cables and products support which features — so far the naming schemes and logos have been rather unfriendly for casual glances. Mandatory cable and port coloring, as was the case with USB 3.0 ports, could help, but it kind of defeats the whole purpose of this one size fits all solution. An even more strictly enforced standard is needed to help consumers get their heads around compatibility will help.

Related: Why are phones still shipping with terrible wired charging speeds?

Unfortunately, the USB-C ecosystem is just as convoluted in 2021 as it was when I first looked at this issue back in 2018. The announcement of USB PD PSS, USB 3.2, and USB 4 make the USB-C port more complex without giving the end-user clear information about what’s supported. While the growth in USB Power Delivery support is a good sign, the introduction of PPS has already hampered any hopes that the industry might soon coalesce around a single charging standard. The USB spec changes every year, making it impossible for consumers to keep up.

Looking for some more data-based analysis else to dig your teeth into? Check out some of our testing content below:

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