Replacement Power Supply Options

So I am pretty sure the iMac im working on has a faulty power supply. The original 240W power supply shows a trickle charge (1 led) when installed, and when you try to power on the computer LED's 2 and 3 flash quickly (less than 1 second) then all 3 go out. I purchased a replacement PS 614-0432 which has all the same connectors, but is rated at 250W. After installing it I believe the replacement is defective anyhow (2nd hand part) as I don't even see a trickle charge LED.

After doing some looking I see it's next to impossible to find an original 240W power supply (614-0405). I see lots of people recommend the 661-4478 power supply which is also rated at 250W. I was wondering if anyone has replaced the original power supply with a newer higher wattage PS without any issues, I'd really like this to work on the second shot. Any insight anyone would have would be great! Thanks!