I also thinking about building my next Hackintosh in a G5 case, but would like to keep the power supply in the bottom case compartment.

So, I am wondering if using a 1U Server PSU will work?

Perhaps something like this DYNAPOWER DP-1U46 460W:

http://www.newegg.com/Product/Product.asp?...N82E16817255003

be carefull with those PSU, the fan can become really noisy when it gets hot :-/

this is meant to work in isolated room no in a room ^^ i got 1 one those (220W), i used to have a P3 733 with a gforce 2 mx400 tv out in a small htpc case and the psu started to make quite some nosie after running for 1h (PC was warm so fan was at max speed)

also notice that the minimum efficienty of this one is 65% this min you're only sure to get 300W.

i'll recomend using a normal PSU and making more modding to make it fit because it could be pretty bad with 300w if you plan to use a recent 3D video card

Yes, I think I would rather buy a regular ATX PSU (they are much cheaper), remove the PSU guts from it's case and put them in the bottom/PSU compartment of the G5 case like TribesMan did with some extra 60mm fans: