Editor’s note: This is an updated version of an article first published in 2018.
USB-C was billed as the solution for all our future cable needs, unifying power and data delivery with display and audio connectivity, and ushering in an age of the one-size-fits-all cable. Unfortunately for those already invested in the USB-C ecosystem, which is anyone who has bought a flagship phone in the past couple of years, the standard has probably failed to live up to the promise.
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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 problem is that the features supported by different devices aren’t clear, yet the defining principle of the USB-C standard makes consumers think everything should just work.
A good example of USB-C problems: Charging speed
The charging example clearly demonstrates a very common frustration with the 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 charger that supports Qualcomm’s Quick Charge or USB Power Delivery.
We’ve tested this numerous times in the past and found that phones from popular brands, including Samsung, Huawei, and LG, all slow down their charging speeds once you begin to mix and match cables and chargers.
Exploring a wider range of devices has revealed some even more drastic disparities between supported speeds and standards. OnePlus handsets, for example, fail to charge quickly at all if you deviate from the provided cable. Fortunately, phones from other brands, such as the Huawei Mate 20 Pro and LG V40, continue to support faster than basic charging when mixing and matching USB cables and accessories, but the support varies quite widely.
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.
In addition to out-of-the-box technologies, USB-C devices can also charge using the optional USB Power Delivery specification, as well as with third-party fast charging solutions like Quick Charge. Many third-party chargers use these standards. However, many cables don’t support Power Delivery’s higher currents, and it’s even rarer to find ones that support the very high power charging needed for laptops.
This year, we have explored the discrepancies in charging support for Power Delivery and Quick Charge standards. We’ve also compared this to boxed charger speeds and support from generic USB 2.4A ports. You can find the data in the table below. Results highlighted green provide good fast charging support, while yellow indicated an OK implementation, and red a failure to support the standard in question.
Support for USB Power Delivery and Quick Charge specifications has improved
Support for USB Power Delivery and Quick Charge specifications has improved with more recent smartphones – a very promising sign. This could in part be due to Quick Charge 4’s compatibility with Power Delivery. However, the mixed bag of results highlights the broader issue perfectly. Smartphones often hide support for these standards in a spec table somewhere and even then there’s no guarantee that consumers know what these standards mean. Furthermore, there’s a huge variation in charging speeds across these devices. Even if a phone supports both third-party standards, they may charge significantly slower than when using the boxed charger.
Yes, there are cable and power adapter labels, but very few consumers check for them, even when displayed correctly. Ultimately there’s very little consistency about the type of charging available. This becomes even less clear when products start using bi-directional charging capabilities, such as charging your phone from your laptop’s USB port.
There's no way to tell if a USB-C/A cable supports high current charging or 3.1 data speeds just by looking at it.
More than just charging: Data transfer speed
It’s the same situation when you look at data transfer speeds. USB-C adapters support 2.x, 3.x, and Thunderbolt speeds for some ports, yet cables also have to be specifically designed to meet higher speed requirements.
The introduction of USB 3.2 and its ridiculous Gen1 and Gen 2 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, essentially a royalty-free Thunderbolt 3 rebrand, drained any remaining comprehension from consumers and developers alike. While the greater numbers do generally indicate faster speeds, there’s little way for consumers to figure out what they need without wading through this branding quagmire.
The USD data naming scheme is undoubtedly a mess. This table below will hopefully help to sort out what each specification offers you.
|Generation||Specification||Optional Consumer Branding||Dataspeed|
|USB 1.x||USB 1.0||Full Speed USB||12 Mbps|
|USB 1.0||Low Speed USB||1.5 Mbps|
|USB 1.1||Full Speed USB||12 Mbps|
|USB 2.x||USB 2.0||High-Speed USB||480 Mbps|
|USB 3.x||USB 3.0||SuperSpeed USB||5 Gbps|
|USB 3.1||Superspeed USB+||10 Gbps|
|USB 3.2||USB 3.2 Gen 1||SuperSpeed USB 5Gbps||5 Gbps|
|USB 3.2 Gen 2||SuperSpeed USB 10Gbps||10 Gbps|
|USB 3.2 Gen 2 2x2||SuperSpeed USB 20Gbps||20 Gbps|
|USB 4||USB 4.0||40 Gbps (Thunderbolt 3)|
Devices and cables are just as problematic when it comes to support for “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 specification, as the capabilities and needs clearly vary from device to device. A USB battery pack doesn’t need to support HDMI, for example.
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 certain Type-C ports on the device, so 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-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. Product spec sheets can help out in this regard, but USB features are often omitted except for the port type. 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.
Port shortages are a problem
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. However, 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.
It’s a similar situation with a number of the latest laptops on the market. Ditching the power socket for USB-C instantly reduces your peripheral count when powering up the device, which is particularly frustrating considering most laptops only have a couple of available ports to begin with. Users are increasingly forced towards dongles to connect up to legacy ports that are still ubiquitous in other marketplaces.
Part of this is due to the fact that although USB-C has made its way to laptops, it’s still notably absent from mainstream displays and common accessories. All the new port has done is move some components out of the laptop and onto the other end of the cable. Not exactly a consumer-friendly move, given the prices often charged simply to regain the functionality of older products.
Trial and error is often the only way to figure out what a USB-C port supports.
Why the compatibility issues?
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 increases 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.
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. This is why some longer cables from third parties won’t 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 redrivers 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.
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 connectors 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.
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.
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, you’ll often see multi-port devices only offer a single Power Delivery port dedicated to charging the device.
USB-C will remain a mess
USB-C’s complexity is undoubtedly 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.
At the same time, product developers are facing a similarly frustrating situation. Supporting the full range of advanced USB-C features is a complex engineering feat, far more so than previous USB generations. Furthermore, the increasing number of components and connectors is raising development costs and deployment time. While there are now more integrated ICs to ease development, the sheer range of options and features in the latest specification makes implementation expensive and time-consuming.
Not all USB-C ports or cables are equal. Unless that's addressed, consumers are going to experience headaches.
Product developers and the USB Implementers Forum need to get on top of this situation and push the standard in a more consumer-friendly direction. 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. Either way, a strictly enforced standard to help consumers get their head around compatibility will help.
Honestly, I can’t see an easy way out of the mess the standard is currently in. The more recent introduction of USB 3.2 and USB 4 is only making the standard more complicated and less user-friendly. Hopefully, we won’t have to wait until USB-D before this situation is solved.
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