Just to follow up ...
Is there a particular reason that you need this fuse information? I hope that there is no plan to replace the car charger with something else. The charger/cord assembly for the 720 is VERY specific in its design, providing a special 'return' wire to the charger to advise of the actual voltage at the unit. Mess with that, and things go very badly.
Ah, very well then. Funny that the fuse was unmarked. Bad form, actually!
If your engineering was in electrical, you may be familiar with the term 'remote sense' on a power supply. That's where a 3rd wire in the older TT cables is used to monitor the voltage at the 'receiving' end to assure that the voltage drop through the power wires is being accounted for and the output of the cigarette lighter supply adjusted accordingly. That's what the 3rd wire in the cable is all about. Guess it allowed TT to use a somewhat lighter and more flexible cable? Never understood that one.