RE: Trouble with XPS 15 9550, USB-C/Thunderbolt 3, and external monitors
Hi. Some conflicting information: Like you, I have my "set what happens when lid closes" setting on "do nothing" for both battery and AC power, but I still have the problem that with the lid closed, the monitor blinks off for about five seconds and then back on, repeating that miscue every 3 to 4 minutes. My experience has also been that the issue has nothing to do with the TB15 dock. I can also use a DisplayPort connection that starts with an adapter plugged in to the USB-C/Thunderbolt 3 port. I have the same problems in that configuration as I do connected to the Dell Thunderbolt Dock.
So, that said, if you have solved the problem, can you think some more about how you did it? I'm sure that all of us and many more besides would really appreciate your information!