Need help identifing faulty componet on full start up failer.

iMac 20.2 Model A1174 2006 last 4 of...

I just installed a replacement power supply on the iMac 20. It's doing the same thing it was doing as before I replaced the original power supply. It powers up then begins to load the OS. After about 20 - 35 sec. The iMac then just power off completely. It will continue to do the same thing after it is powered up again. Turns on, partial OS loading, then powers off. So I'm wondering if anyone have seen this before and could direct me to the faulty part. From what I saw on you-tube and what people posted, I really taught the power supply was faulty. I would appreciate any help anyone can give me. Thanks.