This part was designed specifically for the PSU that came with my Chinese Prusa i3 clone.
The dimensions for the PSU are - 42mm x 99mm
Since I printed this I have added a captive M3 nut on the inside and have added 3 holes to route the wires to the control board.
The holes may be out of alignment for the switch (but not by much)
I printed this switch hole face down and used supports so the captive nut area prints well.
As I have added support around the holes you may wish to support these too
This was designed using Sketchup Make 2017