car chargers?

Sorry if this is a silly question, but would car chargers be the same there? Say for an MP3 player?

Yes

somtimes I find they don't fit 110%.  in my experience they've always worked enough to charge, but it may take a bit of fiddly, pushing on it, rotating it, to get the magic charger working...

Yes, they'll work just fine as it's the same 12-volt electrical system in cars.  The only time you'd have a problem is in a classic/vintage car (1960s or earlier) which might be positive chassis or 6 volts.

The cigarette lighter plugs are often a little touchy on both sides of the Atlantic.  A few pushes in and out combined with a slight twisting motion will often clean up the contacts and improve the connection.

Thank you!