The buzz makes the surface of the 3D printer feel rough when 5.5mm power plug is inserted, whether the on-board power switch is on or off. Once the plug is pulled out, the surface feels smooth again.

And tens of volts, even close to 100V, have been measured by others between the chassis and ground – and it has crossed my mind that the USB input of my PC might be taking strain when it is connected.

Anyway, I suspected the 12V 7A lump-in-a-cord mains power supply (branded GVE and Fo Shunde Guanyuda) to be responsible – too-large or lop-sided Y-capacitors possibly?

So I replaced it with another supply – a Chinese-made 12V 10A, supplied and branded by German firm Leicke.

Result: tingling buzz gone, and diminished uneasiness.

Excellent.

BTW, both supplies have, as far a as I can make out, a full set of CE and UL markings.