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I need a USB-c to HDMI and Ethernet adaptor, what features or protocols do I need to look for, for it to be compatible with Ubuntu 16.04 on a Dell XPS13 (or newer) to drive screens at high resolution?

Some adaptors for sale refer to "DP alt mode" (Display port?). This answer refers to a device not being "displaylink" as the reason it doesn't work.

My question is - what should I be looking for to have a reasonable chance of getting a device that is going to work. What is DP alt mode, what is Display Link in this context?

My Laptop is a 2017 made Dell XPS13 (9350 I think) running Ubuntu 16.04.

I have tried a few adaptors that my colleagues already owned, none are quite what I want - but if I order an untested device - how can I tell if it is likely to work under linux.

The Dell DA200 did not work with HDMI, exactly as described in this question - same question reference above. Although it did work with USB. The Apple Digital AV Multiport Adaptor worked out of the box with HDMI and USB - but doesn't have Ethernet and the USB-C charging port is redundant - as the Dell charges with a barrel jack. This fairly generic HooToo multiport adaptor worked with HDMI and USB - but doesn't have Ethernet.

I've also seen these similar questions, none are quite duplicates.

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I found this question in my search for advice on upgrading to a dual-monitor dock, and thought I'd share what I learned.

According to this article from 2016, "Alt Mode" uses USB to send HDMI or DisplayPort protocols, but the USB standards body does not write a standard for Display Alternate Mode and there are multiple companies that define their own versions. So, according to the article, products using "Alt Mode" can be pretty hit or miss on whether they will work with your particular rig. This reflects my own 2019 experience with HDMI Alt Mode docks on my Miix 510 with Ubuntu 18. Some just work, some do not, and in general the manufacturers don't provide drivers to help. My old single HDMI dock used Alt Mode, but I have yet to find a dual display version that works for me.

DisplayLink, on the other hand, is an individual company that certifies products using their standard, and distributes updated drivers to work with those products on multiple OSes, including Ubuntu (linked above). For my money that makes it a safer bet. This week on Amazon I'm seeing dual-4k and single 5k docks that use DisplayLink, and the latest drivers on DisplayLink's website were released last week for Ubuntu 19.

So, this question is still relevant. Hope that helps somebody.

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So it seems this is difficult to guarantee, but Display Port Alt-mode is a good indicator if you can see that on the specs. But to be sure, you need to find someone who's already reviewed one on your hardware and OS, or borrow one to try in person before buying.

There's a bit of a write up on Display Port alt mode here but the gist of it is that USB 3.1 type-c (usb-c for short) has 4 channels (each a pair of wires), and can assign 1 or more of these channels to carry a different protocol (for example, display port).

The famously non-functioning Dell DA200 apparently doesn't do this - but uses some kind of video over USB fallback, and is hence limited by resolution.

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I am impressed that displaylink has Ubuntu drivers, and up to date. https://www.displaylink.com/downloads/ubuntu not too expensive either. https://www.ebay.com.au/itm/4K-HDMI-Universal-Docking-Station-USB-3-0-DisplayLink-HDMI-Dual-Video-Display/153541111567?hash=item23bfc36f0f:g:uVkAAOSwN6FdEKwD my experiences vary, I have purchased a few of them. One good one, type-c to hdmi, usb 3.0 and another type c port, DIED this week after 40 times used. the type c port that it had would not accept another video, type c to hdmi, so I could only use one video out of it, and another usb 3.0 to hdmi from the laptop gave me 3 monitors. so if it doesnt DIE on you after a short time like it did to me this was it. ethernet can be usb3.0 into it. or type c to ethernet through it. that one is no longer listed, but this one would likely be it. https://www.ebay.com.au/itm/Type-C-USB-C-to-female-Data-USB-HUB-4K-2K-HDMI-Type-C-Charge-Port-Adapter-Cable/182783727141?hash=item2a8ec25625:m:mrOlSYv_--X0kuy8KRTib9g

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With Ubuntu 18.04, I just tried a series of docks via Amazon purchases, and found all of them lacking in dual independent external displays. Some displayed nothing, but most displayed duplicate external displays (show up in the settings as just a single). I have/am returning them all.

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