Keep From Getting Shocked! The most popular 12 Volt Power Supplies used have an exposed 115 VAC to 230 VAC Live Terminal Exposed! This Cover is easily printed, has snap fit retention (no screws needed) and is available with or without a switch hole. Few things on Thingiverse can actually save a life, this is one of them. The life you save, might be your own.
Print, feed your wires through the wire hole, and install.
If you print the one with the switch hole, I use a standard (extrememly popular) size. The hole is for switches that need a 20mm x 13mm. If you want to change it, I have provided both the Google Sketchup File and STL Files for both.
If you do use a switch, I would recommend the supply side live 115 - 230 VAC switched.
The hole for the wires is large enough for any wires you will install, but small enough that little fingers can never touch the live line.
If you need help how to hook it up, here's a video at http://www.youtube.com/watch?v=27lcqgOBb2c