... the GND-potential of your power supply and the PC is off some Volts -- so when connecting with the GND-pin of your USB-cable, a high current peak across the USB-shield will kill the USB-connection.
With a metal/conducting object you'll interact with this potentials too, so again a voltage or current spike will run havoc and again killl the USB-connection.
Measure the voltage between GND and the shielding of the PS, and the housing/GND of your PC against the line ground - there seems to be some weird ground connections with high currents shorting through your cable shields ...
With a metal/conducting object you'll interact with this potentials too, so again a voltage or current spike will run havoc and again killl the USB-connection.
Measure the voltage between GND and the shielding of the PS, and the housing/GND of your PC against the line ground - there seems to be some weird ground connections with high currents shorting through your cable shields ...