I bought a new D6000 Universal Dock to use on my XPS2720 AIO desktop to extend to a pair of DelU2711 displays, replacing a Toshiba U3 Dynadock (it couldn't do both display on 4K). Both screens are running on 2560x1440 resolution, connected by DisplayPort cables. Resolutions & colours are fine, but one screen is constantly flickering & the other 'blinks' about every 30 seconds or so, almost unusable. I have just done a clean Factory Install of the XPS 2720 (updated the 8.1 to 10 Pro again) & updated all drivers, but problem persists.
I have a similar problem. I own a Dell 5285 and am running 2 Full HD Dell monitors and a 3rd 19" Dell 1280x1024 or something like that monitor. When my computer wakes from sleep or I come back from a meeting an plug it in, quite often the 3rd monitor attached to HDMI which runs through the Intel Driver (not DisplayLink) likes to flicker constantly. Most of the time it seems to fix itself if I unplug the monitor and then plug it back in. Perhaps you can try that. That said, thing is supposed to run 3 4K monitors, and it can't even seem to handle 2 FHD and 3rd much lower resolution monitor properly. Dell, please fix this!!! Also, why the HDMI port not source enough current to start up an HDMI to VGA adapter. I have one the can additionally be plugged into a USB port for power, and once it starts will keep running if I disconnect the USB, but it won't start on it's own. Please Fix!