Call me crazy, but I use 3amp quick-blow, quick reset fuses on all of my transformers and DCS Remote Commander, and TVS's in ALL my MTH loco's, be them PS1, PS2 (3V&5V), and PS3.
I'd rather be resetting the 3amp fuse time and again than shelling out for new circuit boards (if available).
I can run my early Buco open framed armature loco's through my early Buco transformer (0-22VAC) and I have never had the 3amp fuse "pop" under load. Only if the loco derails (as they sometimes do) does the 3amp fuse "pop", and I have to wait a couple of seconds to "reset" it.
Cannot emphasize enough the words/advice of Vernon.......get quick acting external fuses on your layout!!!!
Peter.......Buco Australia.