I suspect that without complete galvanic isolation (which would require a transformer in the power supply), you can’t avoid this phenomenon.

Although why you can avoid it probably depends on what country you’re in. But as a general rule it pretty tricky to get a true “zero volt” reference out of an AC socket. (You can’t know if the neutral is actually zero-volts, or just a different phase, or if a fault elsewhere has caused your neutral to drift slightly. Equally you can’t rely on the ground, because if you started leaking current down it, it would trip the ground current leak protector and turn your house off).

Which means the ground the power supply presents to the device is alway gonna be a little bit off.

But laptop chargers _do_ have transformers, and inductors for that matter -- they're switching power supplies! I actually had a problem with this on my MacBook to the degree that I would simply connect a wire between the protective earth and a radiator I had. It worked, strangely enough. It's also perfectly safe to do.

I stand corrected, the power supplies you find for electronics do have transformers in them that provide galvanic isolation.

I guess I’ve spent too much time looking at high voltage (measured in kV) power electronics used in HVDC transmission, it didn’t occur to me that household electronics would use a slightly different approach.