Happy (almost) owner of XPS13 9350 for 2 years now. Since I got the laptop planning to use it with a 4K external monitor most of the time it is essential to have this working properly.
Unfortunately it turned out that the XPS13 9350 has a major hardware design issue with the Thunderbolt port as many of you probably already know. When connecting external monitor the TH3 link is unstable and the external monitor flickers randomly making the experience very unpleasant. My setup is Windows 10 Home x64, Thunderbolt adapter Startech TH3 to DVI, DVI cable to Samsung 4K 60Hz monitor (also tried Startech with TH3 to HDMI, same flickering).
Since 2016 many driver updates from Dell were released specifically targeting the Thunderbolt port, also some ideas from the community suggested to change the wifi card (which I did, now is intel 8265 dual band) and reduce the wifi power output. Eventually I got the external screen working stable with a very simple solution - cold start the laptop, first log in Windows and then connect the thunderbolt cable. If I restart the laptop (hot start) with the TH cable connected, the screen flickered.
Fast-froward to yesterday. Windows 10 forced on me the Creators update (1709). The screen flickering is back. There is absolutely no way to control it now. Rolled back the Windows version (to 1607) and the screen was stable again. Then Windows forced the 1709 to install itself again and the external screen went back to flickering. In my next attempt to switch back to the previous version the Window 10 entered the dreaded boot loop and everything went FUBAR. Had to reinstall the Windows 10 and all drivers. I had a small hope that this will somehow help. Well, it didn't. Screen still flickers like crazy.
Attention Dell Support, please look into what the 1709 has messed up the TH3 port and hopefully a driver can be issued fixing what W10 Creators edition messed up.
Fellow users, any ideas?
I've been dealing with this since October 2016. There is no solution. As you noted, it's better, though not fixed, off a cold start.
Well back in late 2016 I was actually able to achieve the stable external screen state with the "cold start" prior to the forced "down the throat" 1709 update. With the 1709 now live even the cold start is broken. I ended up completely wiping the whole system and reinstalling the 1709 from scratch with all latest drives from Dell. No joy.
Tried fiddling with some BIOS TH settings. No joy. Tried the TH3 firmware 16 (A06) as well as the newer 26 (A07). No joy.
I have noted that the screen becomes more unstable with the increase of the network traffic once connected to the internet to a point of constant flashing when a heavy download is in progress. On both WiFi connection (reduced to 50% output power) or through USB/Ethernet adapter to a network cable the situation is the same.
By the way multiple users outside Dell forums are reporting issues with the 1709 and their external screen connections. Now I am considering downgrading the windows to 1706 or even 1703. The only issue is that Windows will try and probably succeed forcing back the 1709 at some point....
I have this issue as well. I solved it by giving up on Windows and switching to Ubuntu. (I realize this is not a solution for many people.)
The fact that this setup works on Linux and not on Windows indicates that Windows - perhaps Windows 1709, as you experienced - is the issue, not something from Dell.
Obviously Dell is a Windows-first brand and their hardware SHOULD work on Windows... but if it works on a previous version of Windows and not the current version, shouldn't we be posting on a Microsoft forum?