Steps to get your adapter working if you just upgraded to Mac OS 10.11 El Capitan.
Reboot. As soon as the screen goes black, hold down "Command" and "R" until you see a black screen with an Apple logo and a white progress bar. Let go, and wait for your computer to boot into recovery mode.
From the top bar, select "Utilities" and then "Terminal"
In the terminal, run csrutil disable.
From the top bar, select "", then "Restart"
When you boot back up, you'll have a working adapter!
Definitely take a read down below to see what's changed in El Capitan, and if disabling SIP makes sense for your setup.