I too am interested. In my case how to access a say, external hard drive ( easily ), from my house stereo in mp3.

I don't know if this is in the right place or if it will be useful But I recently repaired a broken mouse reciever ( snapped off usb jack) and  thought I would try to post this repair. I will post a pic with instructions.

Just a thought  go to a welder supplier web site (like lincoln or miller) and look for the owners manuals section.  in them there will be a schematic and it give you an idea what's going on inside the xformer. but you may have to look at a few to find a x former that has the same lead configuration...