"I had the understanding that a computer power supply takes in 110 volt house power (twice that in Europe), but then converts it to the low voltage used by the computer - typically about 5 volts. I don't think a computer power supply should have voltage higher that the voltage of the house power."

Computer power supplies are Switched Mode Power Supplies. They take the mains voltage, rectify it, sometimes double the 110 to 220, filter and chop it at a high frequency, transform it to a lower voltage then rectify again and filter. Regulation can be at the output stages or around the whole circuit. Computers use +5v, -5v, +12v and -12v (and often 3.3v at the processor). The first stages of the power supply can and do produces high voltages which are stored on capacitors.

On top of this the common rail often floats at half the mains voltage because of filter capacitors connecting live and neutral to earth. This is very high impedance but is responsible for the tingle you sometimes get from equipment using switched mode power supplies.

MTB