I evaluated different PSU mounting brackets and found http://www.thingiverse.com/thing:1636876 to be a simple and elegant solution. The thing is: it does not fit my PSU. I decided to create a customizable version so everybody can now make a pair for their specific PSU. To make the brackets fit your PSU, measure the following values and enter them in the customizer:

• the distance between the mounting holes on the PSU;
• the diameter of the PSU and frame bolts.

Open the customizer by clicking the the Customize-button, then launch the customizer app. Edit the other values in the customizer when needed. Print two with a higher infill like 30% or 40%. First mount the brackets to the frame. I used M5 post assembly T-nuts for that (check the photo's). After that mount the PSU.