I've bought a couple of similar chargers for GPS on bike and car, and I'm quite happy with them.

http://www.ebay.com/itm/Car-Charger-Adapter-Garmin-Nuvi-205W-650-660-680-2A-/330670115726?pt=LH_DefaultDomain_0&hash=item4cfd798b8e

On the Concours, it's hard-wired so this is not applicable. In the car, it plugs into the cigarette lighter adapter and that seems to have caused a failure

There are 2 springs on the outside of the charger that make contact with the lighter socket ground. One of these is the electrical ground for the charger, the other is not connected to anything.

Inside the charger, the side spring presses against a little plastic nub. On the side with no connection, this nub cracked off, allowing the top of the spring to protrude inwards and press against the glass of the fuse.

When the charger is inserted into the cigarette lighter socket, the internal fuse is pushed inward against its spring, exposing the hot end of the fuse. The side spring, which is now grounded by the socket, contacts the hot side of the internal fuse, and blows the fuse in the car.

My solution for the moment is to remove and discard the side spring with no contact. This also reduces the force on the other grounded spring, hopefully protecting its plastic nub.