Power Supply

Any slim power supply will probably do. The tower Macs are thirsty, fortunately the iMacs aren't too bad, but you will still need a lot of 3.3V. (That's why we can't use the original Sun power supply - no 3.3V back in those days.) I used this one from Dell but it's not that important which one you use as long as it has enough clout to drive the motherboard AND it fits the box. These are available on eBay for peanuts.

The main mod here is persuading the Dell PSU to talk to the iMac motherboard. If you make a mistake at this stage you will let the smoke out big time and that will be the end of this project. The pinout details are below.

This is why you saved the connector from the down converter board. Cut off the dell ATX and CPU connectors and carefully solder the wires onto the pins following the chart below. Heatshrink tubing helps. Here is the connector viewed from both sides before being attacked with a glue gun.

Dell has to be different and use an odd connector for the CPU 3.3V. Doesn't matter, as we won't be using it anyway. Here is the finished octopus in all its glory. The CPU 3.3 connector is bottom right, the blue/white 3.3V wires are now on the iMac connector, top right.

chart here and xl download coming soon!