The PSUs aren't backwards compatible, just forwards. So you can't power a fat 360 with a slim PSU as it doesn't output enough power, however you can power newer 360s with older PSUs. What this means for you is that since the Jasper is the newest fat 360 mobo, you can power it with ANY fat PSU. Check out eBay, Craigslist, or Gamestop if you want a used one, new you can probably find on Amazon or maybe even on Microsoft's website. Me personally I like to get the 203w ones, they're the oldest ones and thus the most compatible - you can power any 360 with them, including slims if you buy an adapter (though the latter point holds true for all PSUs). However, you'd want to look for 203w, 175w, or 150w ones, all of which are compatible with the Jasper mobo.