Car charger requires the adaptor

[ThePeter]

I ordered a car charger that I thought was specific to HTC, but what I got instead was a generic charger that would work on Motorola, Blackberry, etc phones. When I plug my phone directly into this charger, it doesn't charge at all. That is, the little battery icon doesn't change to a plug, nothing. The same thing happens when I plug my phone into the USB cord that I plug into my wall adapter.

However, in both cases (wall and car) when I use the adapter that came with the phone (it has the ports for headphones on it) the phone will charge.

Is this normal? When I was in an Alltel store, none of the car chargers they had would work either.