Regarding power.
All modern computers use switchmode power supplies for their main supply to +-12V,+-5V and +3.3V. These work by:
Rectify AC to DC - Convert to square waves @10's or 100's of KHz - Transformer - Rectify. The conversion to square waves is controlled by the output voltage to give a regulated output. This enables the system to work with a variety of input voltages, now usually something like 90 to 250 VAC.
As the initial stage is rectification to DC it usually doesn't matter what the input frequency is so long as it is either DC or above ~ 40Hz.
The bit between DC and ~40Hz has to do with the HV capacitors in the power supply. Note these are typically charged to 1.4 times the AC voltage ie 350VDC for 250VAC and can remain charged when is AC is disconnected, this is why there are the warnings not to open the power supplies.