G5 iMac - High pitched whine

I have a 1.8ghz G5 iMac with ambient light sensor. When it is on there is a noticeable high pitched whine that is quite loud. It gets even louder if the fan runs more.

If I replaced the fan would this solve the problem or could it be the power supply? Was this common with them?

I muted the speakers and started a game. It is not the fan, but the power supply that is making the whine.

How much is a new power supply for this unit?

17" iMac G5 1.8ghz w/ambient light sensor.