USB WiFi adapter not working after upgrading to High Sierra

After I updated my mid 2011 Mac Mini to High Sierra 10.13.3, my D-Link DWA-171 AC Wifi USB Adapter, which is plugged into it, connects to the internet fine through the SSID for the 2.4GHz band but delivers a "no internet connection due to a self assigned IP address" when I swap it to the 5GHz band. I have tried many suggestions on the net but to no avail. I have deleted preference files from system/library/systemconfiguration as per a number of recommendations to force the Mac to create new preferences but that did not work.