In pursuit of an answer to this question, I purchased a Dell WD19TB dock for my XPS 13 7390 "Developer Edition" running 18.04.3 LTS. After connecting everything, the HDMI external monitor works fine, but the USB 3 and gigabit ethernet ports don't work at all. I looked at my devices->Thunderbolt, and the dock shows up as "pending":
I clicked on the dock name in that screen and this dialog popped up, asking me to "authorize and connect" to the dock:
I click the "authorize and connect" button, and after typing in my sudo password, I got another dialog stating "Failed to authorize device: kernel error."
After this, back on the devices->Thunderbolt screen, the dock shows with an error:
Dell support has no idea what to do with Ubuntu users, it seems, and directed me to the official Ubuntu forum, where I will be posting as well. Do I need to install some drivers for the dock? If so, what drivers and where do I get them? How do I get a Dell WD19TB dock working with my system?