I just replaced a power supply in a 'dead' imac G5 17-inch, that I picked up on Craigslist for cheap, I bought a brand new one off a vendor on eBay, I dont remember the name right now, but it was less than $100, and was new in the box.
It was common for the capacitors in the power supplies of these units would leak and/or explode which was the cause for their demise. It was also common for the caps on the logic boards to do the same. I suppose for $70 for the lot it would be worth the risk.