Dell XPS 13 9380 issue with maxing resolution on second monitor through docking station

@Thomas156  The actual model of that dock is the Dell WD15.  And it's only going to support a single display up to 2560x1600 at the standard 60 Hz.  This is mentioned in the WD15 User Guide available on support.dell.com, and it's related to bandwidth limitations of regular USB-C (as opposed to Thunderbolt) when the USB-C link is set up to also support USB 3.x data, as the WD15 does.  I wrote an explainer post on the various operating modes of USB-C and TB3 with particular focus on their impact on possible display setups here if you're curious.

Also note that since the 9380 only supports DisplayPort 1.2 rather than DisplayPort 1.4, even in the best case scenario, your system would not be able to run that display at its 144 Hz max refresh rate.  You would probably be able to go a bit higher than 60 Hz, but I'm not sure exactly how much.

But in terms of getting the most out of that display that your system can achieve, you have two options here:

• The inexpensive but slightly less convenient method would be to get a USB-C to DisplayPort cable and connect that directly to the system, bypassing the dock.  That will allow the system to send a full DisplayPort interface of bandwidth to the display rather than half an interface as is the case when running through the WD15.
• The more expensive option would be to get a Thunderbolt dock like the WD19TB.  That will allow you to get a full interface of bandwidth to the display because a Thunderbolt dock can tap into TWO interfaces from the system over a single cable (i.e. 4x more bandwidth than the WD15 can access), while still carrying USB 3.x data.