I've see USB hubs with voltages like 5v, 12v, and 24v being made.
This shows 2.1 Amps on USB 3.0
Powering peripherals through USB - Apple Support
USB 2.0, maybe 1.1A.
MacBook Pro (15-inch, Early 2011) - I'm currently running over 1.0A on my USB 2.0 port on a non-Apple device that needs it.
This shows 2.1 Amps on USB 3.0
Powering peripherals through USB - Apple Support
USB 2.0, maybe 1.1A.
MacBook Pro (15-inch, Early 2011) - I'm currently running over 1.0A on my USB 2.0 port on a non-Apple device that needs it.
See http://support.apple.com/kb/HT4049 - USB 3.0 ports on the 2012 models are 5v. USB 2.0 ports on previous machines are 5V as well.
CLinton
USB ports are all 5 Volts DC. Depending on the device, the Amperage (how much power flows) is important. My experience is that iPads need a minimum of .8 Amps DC {800 mA (milliamps)}
From Apple:
USB 1.1 or USB 2 ports:
Up to 500 mA (Milliamps) at 5 V (Volts) to most Apple USB peripherals and all USB peripherals not made by Apple in compliance with USB specifications.
Apple computers with USB 3 ports provide:
USB 3 ports:
Up to 900 mA (milliamps) at 5 V (Volts) to most Apple USB peripherals and all USB peripherals not made by Apple in compliance with USB specifications.
How much power do MacBook USB ports deliver?
