I keep them all in a box.
Whenever one of mine burns out, or gets lost, I go to the box and try to find a replacement. They are all marked with their amp and voltage specs, although its hard for old farts like us to read that black lettering on black plastic.
By "transformer" I assume you mean little AC to DC plugs, with a prong on one end for a wall socket, and a plug at the end of a wire for your appliance.