I love my Monoprice Select Mini v2 3D printer but I decided that having a front power switch and some 5V USB sockets to run lights and fans off would make it even better. So I designed this power console which also includes a cheap 30V voltage/current display to help monitor power use and a simple tool holder on the back.
The design is built on the base connector part which is fixed to the printer using the two rear screws already on the top of the printer column. The circuit is then built in the shell part and I've included my circuit diagram for reference: it's only designed to power cheap lights over USB so you should probably use a better power convertor if you want to power anything expensive from the USB sockets.
Once the circuit is built the two end caps can be glued on, as can the tool holder. I included two cutouts on the tool holder that can be use to glue in 25x10x3mm rare earth magnets. They're very strong and I've even hung spanners from them. The tool holder also includes some holes for things like hex keys and a small file.
When those parts are properly glued, the console should slide onto the base connector using the slots (you'll need to file off any inperfections in the printing of the parts at the slot if it doesn't fit perfectly). It should hold well like that but I included a couple of holes for putting in small screws just to make sure.
I used a 5.5x2.5mm socket for the power input, the same as on the printer. For the power out to the printer I used a 5.5x2.1mm socket to make it harder to mix up the connections. Then I made a cable with a 5.5x2.5mm plug one end, and a 5.5x2.1mm plug the other end, to get power from the console into the printer. The main thing to note about that is the cables take a few amps so will get hot if you don't use thick enough cable (in the photos you'll see I used a number of wires in parallel between the power sockets too, just in case).