Yes, for the Samsung phones.
One story here. I had to get a car charger that put out more than the minimal milliamps that a cheap charger at say a box store had. I found it at Microcenter, but it puts out I think 2 amps without checking. When running GPS and Slacker, the screen is always on, requiring more charging current, it would never charge with the simple USB car outlet adapter as it wouldn't put out more than .5 amps. Not only that, but you could hear the strain of the regulators at work as the noise would transient into the FM transmitter. Ultimately, getting the higher capacity car cigarette USB adapter, allows my phone to be getting charged while using GPS and anything else I want to use at the same time, and clearing up the noise to hear some great beats without the horrible added pitch.
So yes, it will pull what it needs, but it also won't charge if not using enough source capacity either.