The iPad Retina requires 12W to charge.
It appears the Mac has special non-usb-standard drivers that step up the USB 3.0 port to provide the extra power for charging.
My question is: Does a driver exist to step up a PC USB 3.0 port to charge an iPad at 12W?
Best Answer
No.
The iPad charger DOES NOT use a standard USB port, but uses the USB connector to provide a "dedicated charging port". The standard based DCP can supply a maximum of 1.5A. In fact the Apple charger is a non standard device and can supply up to 2A, which it indicates to the device by specific voltages on the data pins.
A USB port supporting data is limited to 900mA.