Summary

The mount for Prusa Mendel, designed for standard PSU. It's placed in left-back, but you can always swap design for another side.

Instructions

Some computer PSUs are useful for Prusa Mendel, you must only make sure it has good 12V rail inside PSU. Single Rail 12V is best choice, not two seperated 12V rails.
Coolermaster has in most PSUs single rail 12V for example.
I use the CM Master GX 450W, which has 35A 12V rail. The PSU seems good tested, it can almost full 100% without blew up, and it's also good protected against overload - which means this PSU cannot blew up. It's also not expensive for quality PSU with high efficiency 80+.
Problem, This PSU has fixed cables. I have designed some parts to make my printer a bit nicer.

The mount part is also designed to avoid blocking the Z-axis part when x-carriage is in Z-min.
You can use the mount for all standard PSU dimensions.
It's easy to mount it on the side of Mendel. It will fit on 2 rods.

Of course there are some PSU mounts, but i like mine more and it holds PSU at better place.

I have also made part for hiding PSU cables: http://www.thingiverse.com/thing:40679
The mount part is made with Google Sketchup.

Prusa Mendel PSU Mount