While preparing to move 600 miles, I was cleaning up some old files and getting ready to backup the hard drive. When, without any indication, the iMAC exploded right in front of me. Smoke, noise and a horrible smell. It ended up being the power supply.
I had worked extensively in the server world and the only MAC experience I had was replacing the hard drive in my MACBook. Since the iMAC was dead, I felt I had nothing to loos. So, I went to IFixIt and followed the steps. I did however remove the hard drive to allow better access to the AC cable. The repair went fine. I followed the steps in reverse and all went well. I still lost a screw I know not where.
As a precautionary person, got the muffin pan my wife uses and as I removed a screw I labeled and photographed each cup with the step it belonged to. It took several pans. I used black electrical tape as the removed tape was useless.