Currently in the process of building C.R.T's S.T.E.V.E CoreXY 3D printer. From the start I decided to customize my build slightly and one tweak was to maximize print area with the specified width and depth of the stock frame. The stock psu safety box is designed so it would sit almost completely within the frame however this interfered with the bed gantry in the configuration I currently have it in so it was time for a remix! Please note that you will still need to print the original lid file to complete the mount.
MonoPrice Maker Select V2.1
PSU rear mount and box .STL files should print fine without supports. The Mean Well RS-150 specific .OBJ file has supports added via MeshMixer because Slic3r Prusa Edition seemed to always want to add supports under ALL the mounts, in the nylock nut recess, in the vents etc. (have not tried printing that version since I was almost out of the filament I was using). If you are using a slicer that can manually add or remove support like Simplify3D or IdeaMaker than print the Mean Well .STL version and add support under the bottom left cover mount tab (when viewed in mounted position).
Since I originally thought I would only need extended tabs (and because I'm still learning Fusion 360) I did everything in TinkerCad. Once I added them and printed some test sections I realized that the mounting holes on both pieces and the alignment nubs on the box did not line up with the Mean Well RS-150 24 psu that I was using. Mounting holes were elongated and enlarged slightly, the alignment nubs were removed from the box, one of the cover mounts was trimmed for clearance (I did it with a file on mine but the change is in the Mean Well specific files) and a recess was added to the lower wall since the mesh cover on the psu sticks out slightly and causes the end of the box to flare out as seen in my photos.