First of all, this is an awesome project. It works beautifully.

I wanted a way to mount my Flex ATX PSU, so I made a couple of models and thought they might be useful to others.

I modified the existing bracket to hold a "double-width" module:

STL here: https://github.com/adamhl8/share/blob/main/LabStack%20Double-width%20Bracket.stl

And then here's a module that holds a standard Flex ATX PSU:

STL here: https://github.com/adamhl8/share/blob/main/LabStack%20Flex%20ATX%20PSU%20Module.stl

Using this in my RackMate T1: