Hi Mark,
The user manual shows the fuse as being item 'C10' but doesn't give a rating....not very helpful.
A supplier (amongst many) for the adapter has an image that shows the unit rating as 1800mA :-
https://kamsat.co.uk/index.php/president-adapter-for-12v-power-supply-and-external-antenna-for-president-randy-3.html
But, they also specify a 'Safety' rating of 5A ???
I would have thought a 2A rated fuse should have been enough but perhaps a Charlie Tango member who maybe owns this radio and/or car kit can confirm.
(If it's just a charger for the radio's battery I would suspect a smaller rating fuse would be used the current draw being 700mA or so then perhaps a 1A fuse.)
Always worth remembering that "fuses" aren't elegant solutions to 'protect' your radio but usually to prevent fires from over current burnouts!
I hope you get sorted.
All the best,
Victor