Support chat helpfully walked me through troubleshooting this. On their remote connection they could see both displays working. Seems maybe I hadn't done the hard reset on the dock correctly (not sure why a reset needed on a newly received dock though). Disconnect EVERYTHING from the dock, including its power cable (I had only disconnected power before). Hold the power button for 30 seconds. Reconnect power. Verify power button blinks 3 times, then connect to computer. Then plug in one thing at a time to see if they work before plugging in the next one. In my case I plugged in the DP first and it came on (as expected). Then I plugged in the HDMI expecting the DP to go off...but it didn't! it worked! I plugged in the few extra peripherals and they all worked. Restarted a couple of times with the helpful Dell remote chat going and the fix persisted. Thank you Dell support folks!
I plugged in my XPS15/9520 to my WD19S dock like I do every day at work and now only one of the connected displays shows up. I have an older display connected via HDMI to HDMI and a Dell U3223QE connected via DisplayPort to DisplayPort. With both connected, output only goes to the HDMI display. If I unplug the HDMI from the WD19S, the DisplayPort connected display comes on. When I reconnect the HDMI display to the dock the Dell U3223QE shuts off and says "no DP signal from device". I thought the issue was the dock but I've just plugged in the replacement Dell sent and the issue persists. I understand you can't have HDMI and USB-C outputs at the same time from the dock, but I've never had that setup and this has worked the past 6 months to output to these displays simultaneously. No changes based on which USB-C port I use on the 9520 either. When the issue first presented I ran through updating everything, including windows and updated drivers for on Dell's site for anything connected. No difference. I have the Dell display manager but don't really see any options there that affect anything. Any ideas on what to try next? Has anyone else seen this issue? When searching through topics here I only find the issue of folks initially trying to use converter cables or USB-C in conjunction with HDMI.
9520 and WD19 dock - only single display output possible