I find myself Googling the same thing right now.
My wife's Garmin power supply went up in smoke...literally....on a trip this summer. The fuse didn't blow, but the wires literally smoked out. It even melted the connecter in the cradle.
I had a friend send me a new power supply, and I hooked it up to my Triumph. It blew a fuse four days later. Pulled the still good fuse from her melted power supply, and it ran for four months until today. Last month I found myself scouring for spare fuses just in case, and never found anyone who carried them.
I've traced every wire and not found a problem. I think it really is just a problem of tiny fuses constantly finding water/mud, etc. But I'm hesitant to throw a larger fuse in there because I can't afford to do damage to the unit itself.
Clinging to sanity, one motorcycle at a time.