Where to plug switch/router/fmc in - on dedicated AC with audio or common line?

Does anyone have any insight if it’s best to plug the switch or other ethernet device on a separate AC line or dedicated line with main audio equipment?

Are ground potential differences not a concern if you put on a separate line ?

Depends, on lots of things. I would suspect the noisy switching power supplies would do more harm than any potential ground loops as they aren’t really in the audio path.

If you have the option, try both and see if you can hear a difference.