It's not a problem with the plug, it will charge an iphone (at least my 4s) The problem is with something else, i think it's a software issue. The iphone can't "talk" with the car using both the blue tooth and the usb at the same time. I can stream audio and make and receive phone calls using blue tooth. I can turn off bluetooth, plug in the phone into the usb jack and stream audio and charge.
I can not connect with blue tooth (so the phone is available for hands free), and plug into the usb port to stream audio/charge. Just doesn't work. I think it's a communication issue where bluetooth trumps everything else if it's on. So i don't think there are any issues with the power available for charging or stuff like that.
I do know my manual mentioned there wasn't enough juice to charge an iPad, but that charger provides 2x the amps of a standard iphone charger.