Once properly installed with 4 screws of a reasonable size, this pair of brackets allows you to easily slide the PSU in and out. You'll need to detach the plug cable from the PSU and pass it through the bracket with a stop wall, before reconnecting it. 

Print the two pieces, as arranged in the provided .3mf or .gcode.

One piece is freely slides along the length of the PSU, the second piece serves as a stop on the side of the detachable outlet plug. 

For PSU size:

3 inch wide, 1 ¼ inch thick, length is adjustable

76 mm wide, 32 mm thick, length is adjustable