U3421WE, longer USB Type-C cable?

@skobzar  A 2m Thunderbolt 3 cable will almost certainly be an active Thunderbolt 3 cable, and active Thunderbolt 3 cables only work as USB 2.0 + power cables when used in non-Thunderbolt scenarios.  The pins within a USB-C connector that carry USB 3.x data and video are the same pins used for TB3 when TB3 is used, and USB 3.x and video are apparently not compatible with the electronics used to create active TB3 cables.  You need a regular USB-C cable that supports USB PD up to 100W rather than just 60W, and USB 3.x Gen 1 (5 Gbps) and video, like this one.  It's 1.8m.  Hopefully that's close enough for your purposes.  Cables that support USB 3.x Gen 2 (10 Gbps) are still limited to 1m today, and your display doesn't support that anyway.  The only exception is an active USB-C cable I know about by Cable Matters, which supports video and USB 3.x Gen 2 over 3m, but it also only supports USB PD up to 60W, whereas the display is capable of 90W.  That said, you really shouldn't rely on the display as a power source for your XPS 15 anyway, since that system is designed for a 130W power source, so even if you get the full 90W from the display, the display will be an undersized power source for that system, which means you can experience slower battery charging and reduced performance.  Dell as of this writing doesn't have any USB-C displays that can provide 130W.  The only way to do that is with certain Dell docks.