While my diagnosis differs from yours, you have done what you can and must now tell Dell you want a refund since their models do not work correctly with these "USB-C to HDMI" devices.
Sad since the XPS 13 is a favorite around here.
I have a Dell XPS 13, model 9350 (released Fall 2015), with the matte 1080p display (non-touch). It has the new USB-C / Thunderbolt 3 port to connect to external monitors. It requires an adapter to connect the USB-C port to HDMI inputs on external monitors
I have purchased two different USB-C to HDMI adapters and have tried connecting both to my relatively new LG LA6900 1080p HDTV as well as an older 1080p computer monitor, both with HDMI inputs. Regardless of which adapter or external display I use, the colors come out washed out with very poor contrast when I export to the displays. Regular greens and blues become neon, the whites are so bright they wash out all detail, browns are a light yellow, etc. In general, the contrast and colors are so off that the external displays are pretty much unusable.
I have used both of these monitors as external displays for several other laptops with no problems. I never have to adjust the monitors’ settings or the computers’ settings. With the Dell, I have tried every imaginable adjustment on the monitors. I have also used Windows 10’s color calibration tool. I have also played around with the display driver’s settings. I also tried using several different HDMI cables. NOTHING fixes the bad contrast and washed out colors.
By process of elimination I know, therefore, that the problem lies in the Dell. I have spent hours on the phone with Dell tech support. They reinstalled and updated the relevant drivers, but to no avail.
Has anyone else expereinced this or have any suggestions? I would really appreciate the help.
My XPS’ specs are as follows:
• Dell XPS 13, model 9350
• Matte 1920 x 1080 non-touch display
• Intel HD Graphics 520
• 8 gigs of ram
• 256 gig solid state hard drive
• 6th Generation Intel Core i5-6200U (3M Cache, up to 2.8 GHz)
• Windows 10 Home 64-bit