I have a 20" early 2008 iMac with a dead power supply. I went to ifixit and they do not have any. Any suggestions on other reputable places to buy such a part?
Assuming you are in the bUSA, here is one on eBay. Check the part number, it does say for an A1224 2008 20" model, and grab it. Cheap as chips and new.
Just on 19,000 transaction and a good feedback rating.