You can look this stuff up on the Internet.
I didn't find anything about an isolated ground, but I wouldn't expect it to matter. The electrical part is straightforward.
I found this for one brand:
Smart Power feature only outputs enough charging power required by the attached device
Energy-efficient, spring-loaded Safety Shutter design turns USB ports off when connecting cable is removed
Also, the USB part seems to be controlled my a chip. My guess is, there's no transformer so they would not have the possible issue of an overheated transformer and fire. That's only a guess.
These still require the USB cable and to turn them off you would have to remove the cable from the outlet as well as the device.
I might install one but I'm not sure if my cameras will charge through the USB port. They are a few years old.