RE: Trouble with XPS 15 9550, USB-C/Thunderbolt 3, and external monitors
I want to add that I had another timeout style glitch.
If I leave my laptop for 10 minutes my screen times out, and goes black. As it should. If I come back the secondary screen won't come on and I have to switch. Or the laptop screen will come on but it won't switch to secondary. The only way to get it to work again is, unplug the dock from the laptop and turn off the secondary monitor. Then turn back on and plug the dock back into the laptop. Select the secondary only and it works again.
Minor issue but it works otherwise. Finally!
I'll keep reporting. I do a lot of programming work so I'm always on my laptop.