When I first installed Ubuntu 18.04 on Dell XPS 13 9370, the DisplayPort's on the D6000 dock didn't work. After a bit of DuckDuckGo'ing, I found installing the DisplayLink drivers here resolved the issue, albeit with a strange issue that when the PC was locked, the screens work randomly flick on and off.

After upgrading to 18.10, the DisplayPorts again stopped working. Again after much DuckDuckGo'ing (and swearing), the following resolved the issue for me.

  1. Uninstall Displaylink Driver package.
$ sudo displaylink-installer uninstall
  1. Run the displaylink-debian script, which installs the DisplayLink drivers, plus modifications to run on most Debian based distros.
$ wget https://raw.githubusercontent.com/AdnanHodzic/displaylink-debian/master/displaylink-debian.sh
$ chmod +x displaylink-debian.sh && sudo ./displaylink-debian.sh

Note: Even though the GitHub page doesn't specifically mention 18.10, this worked for me.

  1. Create the file /usr/share/X11/xorg.conf.d/20-displaylink.conf with the following content:
Section "Device"
  Identifier "DisplayLink"
  Driver "modesetting"
  Option "PageFlip" "false"
  1. Reboot

That is from the DisplayLink troubleshooting page located here.

I don't understand the intricate details of what's happening under the hood with these steps, but they have resulted in dual screens working well via the display ports.

The only possible issue I've noted is that the DisplayLinkManager process can hog CPU. In the instance that it was running at around 150%, a reboot resolved the issue. Anecdotal evidence since then suggests it runs hot when video intensive applications are in use, but I haven't thoroughly tested this.