Originally posted by sylwek
usually its the mobo but it never hurts to check the PS
actually, PSU's are usually first to go (capacitors)
the PSU uses transformers to step down the voltage (consisting of a magnetic loop with coils of wire), then uses a bridge rectifier to convert the AC to DC (consisting of 4 diodes), then the capacitors smooth the power.
the capacitors have to do a lot more in the PSU, because before the capacitors smooth the current, it goes from +XV to 0, 100 times per second.
after the capacitors smooth the power, it will only fluctuate a small amount