OSX: how to determine USB current draw?
Solution 1:
It's not likely that Apple would invest in ammeter circuitry in the usb power lines and connect it to the computer motherboard.
It's likely there is some form of current overload prevention (I wouldn't even know what. A polyfuse maybe?), but it wouldn't be something accessible to the operating system.
Current draw information will more likely than not require additional hardware to obtain.