My two triangles have 247mm between them (to the insides of the 8mm rods), this is designed at 245mm to allow a little wiggle room. My PSU is 150mm (X) between the screw holes, the screw holes are 32mm (Z) above each other.
Overall dimension is 215 x 113 x 50mm

The fused power supply with switch mounting hole is approx 27 x 46mm with two 6.35mm x 6.35 mm chamfers

There is enough room inside to wire up the mains, and the 12V wiring. I have not made a cable exit for the PSU as I wanted to leave this open to wherever your wiring is to go.

I printed mine with support for the top flap that covers the opening, other PSU covers I could locate on thingiverse did not cover this setback completely, which is why I drew this up. Clearance to the Y belt is approx 2-3 mm where it is placed in my photos, I will see how this goes in use to see if the belt rubs at all.

My Prusa has adjustable feet, at the fully wound in stage, the PSU is approx 0.5mm above the table surface.