My DELL XPS15 connects on the go to wireless networks with no problem - eg on campus or at home downstairs. When I go upstairs to my desk and plug in the UD3900 it connects and shows that Internet access is available but I cannot access any websites, send mail etc etc. If I plug in an Ethernet cable I am fine. As soon as I unplug the UD3900 everything works as expected.
I use the UD399 for the multiscreen facilities and additional USB 3.0 connectivity.