Avision AV50F (FF-0803S) - Manual (Page 14)

(2) Supplying the power from a computer via a USB
power cable
Plug the circle end of the USB cable for power into the power
jack of your scanner. Connect the rectangle end to the USB
port of your computer.
Notice:
Using the USB cable for power will occupy an extra USB port on
your computer.
Due to the power limit, the scan speed is lower by using the
USB cable for power than by the power adaptor.
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