I've recently run through very similar steps and and so far it looks like it's more stable. Thanks. One thing I've noticed is that it looks like there should be a light on the cable that plugs in to the laptop but it is not lit when connected. I'm also not getting power over the thunderbolt cable. Are you experiencing the same? Thanks.
Ya, you should have a light. I have noticed it does not come on some times when I first plug it in. I usually unplug wait a few and replug and it comes on. If yours does not do that, I would unplug the TB15 and shut everything down and then repower up.
Updated drivers solve all of the problems posted in this thread. Find the Dell Product Support page showing your specific system including your unique service tag, then click on BROWSE ALL DRIVERS, the select the drivers for DOCKS/STANDS.
Driver versions before March 12 did not stabilize connections, but the newer ones dated March 12 - March 20 did. If this does not solve the problem for you, check your BIOS settings. After downloading the most recent BIOS version, edit the BIOS Thunderbolt settings (F2 when booting) to allow everything Thunderbolt related to work.
My TB 15 is running perfectly including stable USB, Ethernet, and monitor display. I suggest checking that you have the most recent version of BIOS (mine is 1.2.3 released on 1-8-16) and edit BIOS (F2 while booting) in the Thunderbolt section. I ticked all check boxes in the BIOS Thunderbolt section. A separate but also likely necessary solution is to install drivers posted after 3-21-16.
The latest version of the XPS 15 9550 system BIOS is:
Release Date: 05 Feb 2016
Are you sure you are talking about the same Dell laptop?
I have updated/installed/reinstalled/rebooted everything MANY times, following strict ordered instructions from the Dell website (there are actually three slightly different versions if you keep digging, minor ordering differences), as well as a couple from the web (right here included).
The most stable I have been able to achieve still intermittently/ regularly loses the external monitor (Dell U2410) connected via DisplayPort. HDMI to my other U2410 doesn't currently this problem. Seems like the only "reliable" way to get it (DisplayPort) back is to disconnect the dock, power off the dock, reboot the laptop, powerup the dock, and connect the dock. I've swapped monitors/cables/ports - problem follows any DisplayPort connection.
Prior to this I was using a D3100 dock and everything worked perfectly, But it didn't provide power, have Thunderbolt, or USB-C, so I "upgraded" to the TB15 ... which has been nothing but a nightmare.