I was looking for a PSU mount in rear left side of my prusa and all I found doesn't match my PSU, so I decide to make my own design using as reference this one http://www.thingiverse.com/thing:40672.
It works real fine and can be printed with a Prusa 2 (7'5cm high), others PSU mount are too high.
Also I add the dwg file of the design.
Just print it and use the clamps to attach it to the prusa bars.
Maybe you have problems printing the upper clamp, so I add another stl without this clamp. Print this design and use acetone (if you use ABS) or glue to add the clamp later.