All USB ports on a MacBook Air/Pro are the standard 500 mA (milliamps) at 5 V (Volts). However when an Apple device (that require or can use more mA) is plugged in it can output up to 1100 mA at 5 V
This power is available under certain conditions:
- An Apple peripheral device must be plugged directly into an Apple computer or display. Apple peripheral devices connected to hubs will not have access to extra power above the standard USB specification of the port the device is connecting to (500 mA for USB 1.1 or 2, 900 mA for USB 3).
- Your Apple computer or display must be powered on and must be awake. If your Apple computer or display is asleep, all ports will provide their normal maximum output. If your Apple computer or display is powered off, no power will be provided.
- The port providing extra power is determined by the first Apple peripheral or device to connect to the Apple computer or display that requires power beyond 500 mA for USB 1.1 or 2, or 900 mA for USB 3. The remaining ports will continue to offer their normal maximum output. Some Apple computer and displays may offer the ability to operate more than one USB port at 1100 mA at 5 V. On those computers, the second or third port is enabled when an appropriate device is connected.
- An Apple computer started up to Windows via BootCamp will not provide extra power.