A SuperSpeed USB device must draw no more than USB 2.0 levels of power until it is configured as a USB 3.0 device and it has provided its power budget requirements to the system. At that point the system will adjust to meet to device's needs, if possible, or leave it to power itself.
How much more power is available to SuperSpeed USB devices? Six times more than USB 2.0. The maximum allowable current draw on a USB 2.0 port is 150 mA at 5.0 volts; SuperSpeed USB devices are allowed up to 900 mA at 5.0 volts.