I use a 18V supply for my Reprap (to get the heated bed and glass up to temp for ABS). It is the standard metal frame supply you can find on eBay and the like for $55 out of the far east. This cover slips on the front to provide a location to mount a switch and has text formed in the surface to label the On/Off. First print, then mount a standard 5 amp toggle switch you can get from Digikey or Radio Shack and slip in over the front of the terminal area. You will need to drill pilot holes for mounting screws to secure the cover to the supplies side wings. Also drill holes for your 110 cord and DC wires that go to your printer. (See pictures). I use tie wraps on the inside of the cover on the cables to strain relief the cables from being pulled out.

Inventor Fusion file included so you can edit as you see fit.