This is how I modified a power supply to charge my Lipos. This is not a multirotor build but maybe you like my first article anyway.

First of all I had to get a power supply. I got mine for free from a friend and maybe you have one laying around as well. If not, you can find them for very cheap on ebay.
To check if this thing works I used a paper clip to bridge two of the sockets to turn the power supply on. You can find instructions on the Internet on how to do that.
After waiting one day to let the capacitors discharge, I took this thing appart and cut all the unnecessary wires of and desolderd them afterwords. Then I soldered wires to the 5v and 12v terminals. After soldering the on/off switch on, I did a second test. Everything worked and it was time to figure the placing for the connectors out. I made coustum wood parts for the banana plugs the xt60 connector and the on/off switch and glued them in place using epoxy. I even glued a 12V LED strip around the fan to always have some load on the supply and also for aesthetic purposes. After the glue dried it was time to finally mount everything in the enclosure. I soldered all the wires to the plugs and mounted the pcb with a lot of hassle in the enclosure. Then it was time for the final test. Because I didn't trust this thing at first, I tested it with some safety percautions. It turned out that everyting works and now I have power supply for my isdt charger.
The following photos hopefully explain the rest!

Feel free to let me know about writing and grammar mistakes. This is my first article and beeing german doesn't help my language either :)