A few screws later, and....

The power supply is out.

Oooh, pretty colors!

Both the blue and red parts are capacitors. Unfortunately they didn't have enough markings on them for us to identify their capacitance.

Their Capacitance is 27.5 for both reds, the one blue against the board is 15, and the other two visible blue ones are 20. (all in micro-farads)

The power supply puts out 25.8 amps at 12 volts, for a total output of 310 watts. That's the biggest power supply we've seen in an iMac.