If you connect only to the + and – wires, the max you can draw “legitimately” is 500mA. For more current, there is a simple protocol involving switching various resistors across the two data lines. There are easy to use chips which do this. Check out the TPS2511 for a fairly old example. That enables you to build a device which can negotiate up to 2A, at 5V. It is very handy. At work, I was...