It just says "charging" without additional useful details. Other owners seem to indicate on various forums that they see an indicated difference, so I need to do some experiments.

EDIT: if you go to Settings -> Battery, it tells you "USB" or "AC" charging. From this, I can see that the three different chargers I've got at home report "AC". (Well, one of them *sometimes* reports AC and sometimes reports USB.) I'll later try out the car chargers.

Meanwhile, if you do a suitable Google search, several vendors advertise "high power" car chargers. I might need to give one of these a try, but then there's the question of whether I'm getting the Apple (non-)standard or what.