USB adapter stops working after deleting NetworkInterfaces.plist
System Preferences > Network

If you can see your USB adapter in the list unplug it, Delete the entry using the "-" button bottom left of list of devices.

Then plug it back in, if it fails to auto detect then press the "+" button and add your USB adapter.

If it doesn't show your adapter in the list:
then press the "+" button and add your USB adapter.

Only do this if the option above don't work, it could be the permissions have gone awry  on the directory to NetworkInterfaces.plist , in which case use disk utility to repair permissions on your hard drive, select the Volume such as "Macintosh HD" not the physical drive when you do this.
If you are on El Capitan you will need run from teh Terminal

csrutil status

If System Integrity Protection is enabled (which it should be in most cases), then the command output will indicate so. Being enabled will in turn indicate that permissions have been checked and maintained.