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A bunch of details:

  • the USB hub is built in a display Lenovo ThinkVision P27h
  • everything works as expected when a laptop is connected to the display over USB-C 3.1 port on both sides: power delivery for battery charging, video input and 4 USB-A ports HUB
  • another PC is a desktop with USB-A 3.0 and it's connected to the display with HDMI
  • I'd like being able to easily switch between the desktop and the laptop (using one at a time obviously)
  • the USB-A data fallback on the display's USB-C port can be assumed working. Nothing in user manual about this but it's confirmed by users over here with an USB-C to USB-A cable
  • it's not as convenient to switch two separate cables on the display side as it would be to use a single cable with and connect it to either the laptop directly or with to the desktop over an adapter

The question: is it possible to use a regular USB-C to USB-C cable with and USB-C female to USB-A male adapter to have the same setup as with a direct USB-C to USB-A cable? How to choose the right adapter?

I've tried one adapter alredy and it doesn't work. Was it just a bad choice or such a setup simply won't work?

To add one more details. The desktop has one USB-C port as well, although of version 3.0 not 3.1. I thought the USB-C 3.1 cable simply fit into it and all would work without any adapters (for the USB hub purpose only, of course). It appears that the USB-C 3.0 port differs from the 3.1 as the plug is too loose to stay in it. Just falls out and doesn't work at all. Is it expected? Can the USB-C 3.0 be helpful anyhow for setup I'd like to achieve?

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  • "another PC is a desktop with USB-A 3.0 and it's connected to the display with HDMI" - please elaborate what do you mean here. Is the display connected to the desktop via HDMI dedicated ports/cable? Why USB-A enters the picture? – Ale..chenski May 22 '18 at 5:17
  • If the desktop PC is connected via HDMI cable, and laptop is connected via Type-C cable, why don't you simply use the "Switch the video input source" function on the display? Or do you want the USB hub to function on desktop PC as well? – Ale..chenski May 22 '18 at 5:37
  • @AliChen, yes! The last sentence of the last comment of yours - that's exactly what I meant. I should've written a step by step use-case scenario in my question. Desktop remains always connected over HDMI and input selection is the thing. Desktop has it's own power cord too obviously. What needs to be re-attached when switching between laptop and desktop are USB peripherals. So I'd like being able to do it with a single cable utilizing display's USB hub. Ideally with the same cable plus adapter for the desktop as the port on the back of the screen is less reachable than ports on the devices. – topr May 22 '18 at 12:01
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After reading the question few times and looking into the linked thread, the answer is: No, you can't achieve the same functionality as laptop on your "desktop PC", even if it has Type-C (or other USB3) port. The reason is as follows:

Your laptop Type-C port shows functionality of both video and USB3.0 hub when connected to Type-C port on the display. It means that the laptop supports full-featured extended Type-C function, aka "DisplayPort Dock": it has full USB3 (using two differential SS lanes), and two-lane Display Port connection, all over the single Type-C connector. For information, full-featured C-C cable can use four super-speed differential pairs for this purpose.

Your desktop PC doesn't have this "combined" USB+DP feature, it has only vanilla USB 3 ports, both of Type-A and Type-C. None of this ports supports DP function, that's why the display won't work with Type-A to Type-C cable, nor with CC cable. In both cases however you should have the hub functionality, but not video.

The fact of USB-C port being loose has nothing to do with display/USB function nor with USB 3.0 or 3.1. Older (and in general) Type-C receptacles are flaky, loose, and there was some ECN for improvements in spring retention functionality of the shroud, if I recall correctly. Nowadays there is another addition to Type-C connector, connectors with retention screw(s) to solve this general mechanical problem.

In short, the function of simultaneous switch of display and hub using one Type-C cable is impossible with your current desktop PC.

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  • Thanks for taking your time in reading my, apparently not so clearly stated, question and giving the answer. I was fully aware there is no way to achieve the same full functionality on a single cable. What I'd like to achieve with the desktop PC is connection USB-C (display) to USB-A (PC) ONLY for the display built-in USB hub so I wouldn't need to re-attach multiple cables each time for all the peripherals (mouse, keyboard, etc.). Video signal is not an issue. Desktop is already connected over separate HDMI cable so just a matter of selection an appropriate input via display's control menu. – topr May 22 '18 at 11:49
  • Speaking about USB-C 3.0 port on my desktop PC. I wasn't sure if the socket is different by design or is it some flaw. It seems it's the latter according to what you've said. It's a pity as no adapters at all would be needed achieve what I'd like - assuming the display's USB-C is capable of operating in data only mode for the hub while the video goes via other input like HDMI – topr May 22 '18 at 12:05
  • @topr, technically there could be an adapter. There are USB devices of "USB Video Class", who are a sort of stand-alone videocards. They take USB3 protocol, and generate display output. So one can have a dongle with a hub, have this DisplayLink USB device, and then combine its DP output with another hub port within the same Type-C connector, making it like "Display Dock", just as your laptop does. Type-C is just a connector, it can carry many functionalities, and all depends on what is designed into the host end. – Ale..chenski May 22 '18 at 16:45
  • Thanks, but I'm not trying to run video over USB while connecting to the desktop PC as it's already connected with HDMI. I'm only trying to find out how to make the display's built-in USB hub to work given display has only USB-C upstream port and the desktop has only USB-A ports. I would like to know should the hub work (mouse, keyboard, etc.) if I connect it with USB-C to USB-C cable with an USB-C female to USB-A male adapter on the desktop side. – topr May 23 '18 at 17:07
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    @topr, the built-in hub in your display should just work with any properly made USB-A to USB-C cable. – Ale..chenski May 23 '18 at 19:00
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The question: is it possible to use a regular USB-C to USB-C cable with and USB-C female to USB-A male adapter to have the same setup as with a direct USB-C to USB-A cable?

No. The function of a USB-C female to USB-A male adapter is not defined by the USB specification, there's no knowing how these adapters are wired.

How to choose the right adapter?

If you have to use a USB to USB adapter when the cable is not fixed to the device then you are likely doing something wrong. Don't buy a USB cable then buy an adapter, buy the right cable so you don't need an adapter. Unfortunately there's a lot of cables that look like USB cables but are not because they don't follow the USB spec. Look for cables with the USB trademarked icon on it, those meet the spec and are far more likely to work than those that do not.

I've tried one adapter alredy and it doesn't work. Was it just a bad choice or such a setup simply won't work?

It's not surprising the adapter doesn't work. Be thankful no damage was done to your hardware by this adapter. Again, the functions of those adapters are undefined, they might work as intended, they might do nothing, they might short the power supply of your monitor to that of your computer and start burning.

There is a device for switching the keyboard, video and mouse between two computers. It is unsurprisingly called a KVM switch, using one will save wear on your ports, making switching between the two computers as easy as pushing a button, and not involve the use of adapters that violate USB specifications.

To add one more details. The desktop has one USB-C port as well, although of version 3.0 not 3.1. I thought the USB-C 3.1 cable simply fit into it and all would work without any adapters (for the USB hub purpose only, of course). It appears that the USB-C 3.0 port differs from the 3.1 as the plug is too loose to stay in it. Just falls out and doesn't work at all. Is it expected? Can the USB-C 3.0 be helpful anyhow for setup I'd like to achieve?

The specification on the USB-C port was not changed from USB 3.0 to USB 3.1. If the plug is loose then it was out of spec from the factory or became out of spec from wear. Look for that USB icon on cables used for connecting USB devices, if there's no icon then it might not be up to spec.

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  • Thanks for you reply. I'm using a KVM switch now as I have changed monitor since the original question was posted, to Dell U3419W which has a built-in KVM switch. However the issue I was having back then (the loose plug) was due to the fact motherboard ports were not settled properly against case backplate. Basically it was impossible to push a plug deep enough as the gap between the USB-C port and the backplate was too wide. When I fixed that the adapter/cable configurations I had tried before with the Lenovo P27h and described here the issues with, have started working just fine. – topr Jan 4 at 15:36
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Possibly yes. https://cforcedesign.com/products/cf120-central-hub-video-processor-for-cf015c-cf012s however it says

The CF120Pro only works for CF015C and CF012S

Also it has a fan.

Try and report back?

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  • While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. - From Review – davidbaumann Dec 13 '19 at 8:38
  • What more is there to be said? It's called the CF120Pro and it does what OP wants it to do if it is doing what it is doing in a standards compliant way. – chx Dec 13 '19 at 19:14

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