I am not sure if I can provide the exact answer to your question but this is what I have learned. The Tab needs a two amp power source to charge while it is operating. Most USB chargers and ports on computers only put out about .5 amps.
If you power off the Tab and plug it in to a computer USB port, the device shows that it is charging but if it really is, the pace is very slow. I tried to charge mine from the USB port on my laptop after powering off. After two hours of charging, I did not see much if any evidence that the battery level had gone up.
I have not yet found a 2 amp USB car charger that will accept the Samsung power cable but it seems reasonable to me that if you have one of those, you should be able to charge the device in the car. Of course, you could buy the Samsung car charger which I am sure works.