I have a maplin power supply (
http://www.maplin.co.uk/p/100w-slim-bench-power-supply-n93cx) which I have now realised has killed several of my devices, including a few AVR UARTs, a papilio voltage regulator, and maybe more.
The problem is that the negative output is "kind of" isolated - there is significant capacitance to earth. I noticed tiny sparks when connecting it to earth-referenced devices (eg to a FTDI cable connected to USB ground). I have now "fixed" it by connecting the output negative lead to earth through a 10k resistor (there is a grounding terminal on the front panel). The capacitance is significant enough to damage devices, and when I connect a voltmeter between earth and the negative output I have measured >150V! This does not quickly drop through my multimeter input impedance, which leads me to think the capacitance is far too high. With the 10k resistor the output rests at ground potential.
My question is, which of these if any is the "answer"?:
Crappy PSU with high capacitance to ground.
The ground point on the front of the unit is supposed to be used for this purpose.
This is normal with isolated PSUs