I am surprised no one has piped up a little basic electricity here. A device draws the power its can use. The power is regulated to the battery to control the charge. The regulator is in the battery. But a laptop USB port with a power capacity of 2.5w can never provide more than what its capable of. 5 volts at .5 Amps = 2.5 watts. Your wall wart (car plug) is capable of more than that. I have wall warts rated from 10 watts (5V. x 2A) to 5 watts. (5V x 1A).
There must be some sort of use of the data lines to signal to the phone the limits so it can indicate USB or AC. I guess the regulator could be smart enough to conclude which it is based on the initial charge rate which would be the time of highest draw.
So, the maximum capacity of the power source will affect how fast a charge it is capable of, but the regulator of battery will control and limit the power consumed to what it decides is the right level. I have a 12v. 50A power supply to power my 100 watt radio transmitter. I could slap a big 5 volt regulator on it to control the voltage and use some car battery jumper cables to my phone (nice image, eh?) and the phone would be just fine.
There must be some sort of use of the data lines to signal to the phone the limits so it can indicate USB or AC. I guess the regulator could be smart enough to conclude which it is based on the initial charge rate which would be the time of highest draw.
So, the maximum capacity of the power source will affect how fast a charge it is capable of, but the regulator of battery will control and limit the power consumed to what it decides is the right level. I have a 12v. 50A power supply to power my 100 watt radio transmitter. I could slap a big 5 volt regulator on it to control the voltage and use some car battery jumper cables to my phone (nice image, eh?) and the phone would be just fine.