@theruttmeister said in Ground loops don't only affect 3D printers:
The most likely risk is that you get a nasty shock when you touch the now un-earthed case
I said nothing about an "un-earthed case".
Of course you want the AC ground to be connected to the AC ground on any power supply that has such a connection.
You also want the AC ground to be connected to any metal parts (case, frame, etc) in case the AC hot or neutral could come in to contact with the metal parts and thus post a risk of shock.
But the DC outputs of the power supplies, as used in 3D printers, are almost surely isolated from the AC.
And given the low voltage they do not pose a risk of shock.
So there is no need to connect the DC negative output to the AC ground.
Frederick