OK. My coworker just got one of these in, and she let me borrow it so I could test it out. (This is the $3 USB to car charger adapter available from Tasty Vapor).
Input: DC 12-24V
Output: DC 5.0V/500-600mA
I plugged in my 510 PCC (with a battery in it) with the car running, and the bottom two lights turned red. According to the instruction manual for the PCC, this means that the case was being charged, but the voltage was insufficient to charge the battery (3.3V - I think so anyway - the English in the manual can be a little confusing).
I turned the motor off (accessory mode), and the top and bottom lights on the PCC were red, meaning both the PCC and the battery were charging. I found this surprising - when I had the engine running and the battery was not being charged, was this just because I was parked and not actually driving?
In normal circumstances I wouldn't leave the house with a dead PCC and a dead battery, so this would never be an issue. But I would hate to be without a means of charging batteries in the event of a longterm power outage (like 2 years ago when we were hit by Ike).