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I have a Lenovo Legion Y520 15IKBN (the specs of the Y520 are here, I have the one with a Nvidia 1050 Ti), and I have just bought a VR Headset Oculus Rift S which has a DisplayPort connection. I had noticed I might have issues, but then forgot.

The specs say my USB C port is "USB 3.1 Gen 1 / DP 1.2" so I should get it working with a USB C -> DisplayPort adapter. I have just bought such an adapter (this one, actually), but I have read multiple times that it's a lottery and that I might have to buy another one, and perhaps yet another one to get it to work.

Regardless of whether I eventually get it to work, how on earth is that possible? Since the datasheet says it's dual use "DisplayPort 1.2", it should be compatible with any adapter which converts from USB type C to DP, right? Anyone has insight on how the conversion is done, to illustrate?

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  • Perhaps people think the adapter is faulty when using it with VR headsets, whereas often times the USB C which are labeled "DisplayPort" are not routed directly to the dedicated graphics card (only to the integrated graphics card)? Sep 11, 2020 at 17:03

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The problem lies with USB-C supporting so many different video output standards, and different laptop makers choosing which one they support, and if they support one at all.

Take a look at the list of USB-C supported alternate modes: https://en.wikipedia.org/wiki/USB-C#Alternate_Mode_partner_specifications

In that list you will find three video modes, DP, HDMI, and MHL. Then there's two modes, USB 3.x and Thunderbolt, that allows for connecting a separate graphics processor. (There's VirtualLink also listed but that looks like it's not come to market yet.)

So, something with a USB-C connector to the computer and DP for a display can have any of a number of things in between. It can split out the DP from the USB like so many "travel docks" or "mini docks" on the market. It can take HDMI from the USB-C and convert that to DP. It can take MHL from the USB-C and convert that to DP. The device can take USB or Thunderbolt and use it's own GPU for DP output, but these are often quite large and expensive devices that are not easily mistaken for an adapter cable.

Then there are device manufacturers that cannot be bothered to comply with the USB specifications and will make a converter that takes their idea of DP over USB-C and output that as something that may or may not be close enough to DP for your device to work.

I like USB and I think that generally they did a good job writing the spec. The problem is mostly with people making devices that do not comply with the spec. Another problem is USB deciding that supporting three different video modes on one port was a good idea.

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