While Plugable officially supports Linux with many of our products, we do not support Linux with our USB 3.0 docking stations like the UD-3900 and we do our best to call this out in our product listings.
That said and as you mention, DisplayLink (the separate company that makes the primary chip within the UD-3900 and who does all the driver development) have released a driver for Ubuntu Linux on their website → http://www.displaylink.com/downloads/ubuntu.php. As of today that driver is officially compatible with Ubuntu 16.04, 18.04 and 19.04 only, and some of our customers have reported it works with our UD-3900 dock.
Please keep in mind that Plugable does not support using the UD-3900 with Linux, and the above information is provided only as a courtesy. Should you encounter any issues or problems attempting to use the UD-3900 in Ubuntu Linux, you would have to contact DisplayLink directly via email (https://support.displaylink.com/) or via their support forum (http://displaylink.org/forum/forumdisplay.php?f=29) for assistance.