USB-C Works, but how would you Know?

Using USB-C to charge a laptop while simultaneously providing display and other IO traffic sounds a little bit too good to be true in practice.  Maybe it would work for a set of devices from a single manufacturer (like a Thunderbolt-based USB-C-attached dock from the same vendor as a laptop). However, recently I was surprised (in a good way) when it turned out that I had accidentally got myself a USB-C-based single-cable-to-the-laptop setup. USB-C promises a lot, in this case it delivers perfectly, but what bothers me is the fact that there is really no way I could have figured this out ahead of time.


Start with the screen. A while ago, I bought a Dell U2520D 25-inch 2560×1440 display – basically since I liked its resolution/size balance. The screen was billed as a “USB-C” screen, the significance of which was lost on me. I assumed that USB-C was there to provide the normal connection from your computer to the USB hub in the screen. Dell’s marketing materials do mention that you can power the laptop from it, as well as daisy-chain displays, but not to any great depth. Most of the material is about the quality of the panel, the flexibility of the stand, the power of the Dell Display Manager software (which you have to go and download on your own), etc.

I first connected the screen to a couple of stationary PCs at home, and the USB-C connector was more of a hassle than a feature. One brand new gaming desktop turned out to have a single USB-C connector on its back panel (but loads of USB-A), the same as my 2017 home-built living room PC. At least it was possible to connect them at all, and the result was the expected – using the screen as a hub to connect additional USB devices to the screen.  Annoyingly, instead of four USB-A connectors, I got three USB-A and one rather useless USB-C.

Single-Cable Docking

When I connected the display through USB-C to my (couple of years old) work laptop, it turned out it could do quite a bit more than just pass through a keyboard and mouse. It also took care of the display and power – leading to a single cable now connecting the work laptop to the screen, a much more convenient setup than what I used to have.

How I got to this point is the point. In my previous work-at-home setup, I used a 22-inch Dell 1080p screen. I connected my keyboard, mouse, camera, and microphone to the screen, making the screen a virtual docking station. Using the laptop meant plugging in HDMI to drive the display, USB-A to use hub in the screen, power from the standard laptop power adapter, and wired Ethernet for good measure.

The connectors we all understand

This old setup is easy to discover and set up, if a little bit of work each time the laptop is connected. The functionality of each connector on the laptop is obvious, since each one is basically single-purpose and there is no way to plug anything into the wrong port. This is not the case with the universal USB-C connector. A single USB-C connector can be anything from just a power supply for a phone to na all-singing all-dancing Thunderbolt connector.  

Discovering the Features of USB-C

When I first attached the laptop to the screen, I used the same setup as before: power, HDMI, Ethernet, and USB-C replacing USB-A. It worked… or so it seemed.

With both HDMI and USB-C attached, something strange happened to the resolution on the screen. For some reason, Windows drove the screen as 1080p over HDMI… which was odd for a 1440-pixel-high display. Checking the resolution in the display settings in Windows showed that I had two screens attached to my laptop! Basically, my laptop thought it was driving one screen over USB-C and another screen over HDMI. Both of which happened to be the same physical display panel. Interesting behavior, but the laptop really has no way to know that the both physical connectors drove the same display. Thus, I unplugged the HDMI cable.

Next, I went back to the specification for the screen, and finally noticed that it said something about power over USB-C. Not actually expecting it to work, I unplugged the power plug and Windows still showed it as connected to power! Amazing. I also like to note that the hardware did accept having two inbound power connections at the same time without frying – something inside the laptop clearly had been designed to check for such cases and do the right thing.

Removing the Ethernet cable as well and relying on WiFi for network access (a bit less elegant but OK), I was down to a single cable doing both display, power, and USB peripherals.

The remaining problem at this point was that the screen lacked one USB-A port: as noted above, the standard setup is keyboard, mouse, camera, microphone. I solved this by buying a short USB-C-to-USB-A adapter cable, and now everything is attached to the screen.

I did find one drawback with the setup – if I turn off the screen at night to avoid the light from the screen’s power indicator light, the laptop does not get to charge. Minor issue, but a possible problem if you want to have a charged laptop in the morning without the light at night.

How Would I Know?

The problem I have with all of this, and why I decided to write this blog, is that it is incredibly difficult to read the specifications for the hardware involved and deduce that this is what can be done.

USB-C connector, with the Thunderbolt icon

On the Lenovo laptop side, the functionality is part of the Thunderbolt 3 functionality. But the fact that it can bundle screen, power, and USB over the connector is not documented in any clear way. Its 176-page manual has this to say:

USB-C™ connector (Thunderbolt™ 3 compatible) The USB-C connector on your computer supports both the USB Type-C™ standard and the Thunderbolt 3 technology. With an appropriate USB-C cable connected, you can use the connector to transfer data, charge your device, or connect your computer to external displays. Lenovo provides various USB-C accessories to help you expand your computer functionality.

Not exactly clear on what you can expect when you plug something into the port, or what an “appropriate” USB-C cable actually is. It sounds like the idea is that you should buy a Lenovo Thunderbolt-based dock for the laptop (like this one) and then connect screens and keyboards and other accessories to that dock. Easy to understand, good money for the company, obviously, and easy to support (the docks tend to expose the classic understandable ports).

The documentation offers no real help as to what is required for a display to be used as a dock for the laptop. Reading the above, how would I compare it to what the documentation for a screen says to determine if they can work together?

And why did Lenovo decide to have both a regular power connector and the power-capable USB-C connector in the first place?  It seems like it would have been simpler to use a USB-C-based power adapter instead of the power plug – simplifying the hardware as well.


Fundamentally, USB-C suffers from a huge discoverability and documentation problem. How can you know which devices will work with which other devices, and using which cables? As an example, just for fun, I tried connecting a mobile phone charger to the laptop, and that did not work. Why? No idea. We really need something better if USB-C is to really be the one port for the future.

One idea for solving the problem of discoverability would be to have the PC hardware declare its functionality to the operating system in such a way that it can show it to the user. It would be very useful to bring up a system information or ‘about’ feature in Windows, and have it show the ports of the hardware used and the capabilities of each.

Also, USB-C connectors in particular need to be much better documented in terms of what they actually support. Not to mention USB-C cables… I have quite a few of these at home since all the mobile phones in the house now use it, along with some headphones. But the charging speed for the phones is totally random depending on the particular cable + charger + phone combo (well-known issue).

Where are the Devices?

Finally, when are the peripherals going to switch to USB-C?  All phones (except the oddball things that Apple sell) use it for charging and data today. It looks like headphones are starting to move toward USB-C too for charging (all my most recent buys do use USB-C instead of micro-USB). But everything else?

Logitech for some reason has still to release a USB-C version of the universal receiver. It seems like it would a simple and easy thing to do, and all of a sudden a large number of my collection of mice would work with USB-C instead. Keyboards also seem to stick to USB-A very stubbornly, just like cameras, microphones, and hard drives.  Even though most thin-and-light machines are tending towards USB-C-only designs, the peripherals we all rely on to get stuff done are still on USB-A.

For example, I could imagine having a strong mechanical gaming keyboard be my USB-C hub – including powering the laptop and connecting multiple other devices. Maybe the keyboard should be Thunderbolt capable too, and drive the screen?  A screen like I have is a good place to start, but we need the other devices to also use the standard connector is this is to be really useful.

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