Originally Posted by richb500
USB spec calls for 5V, 500mA max output (it's often less - reason is that it's 500mA per hub and in must configurations multiple ports share a single hub internally so multiple devices all plugged in at the same time will share the 500mA).
Actually you got that backwards, its 500mA minimum. Check the docs
if you do not believe me. And before you quote it, yes I do know that wiki says "A maximum of 5 unit loads (500 mA) can be drawn from a port in USB 2.0" that is because they are talking about the maximum that you are guarantied to receive as a USB device. You really need to read both sides of the documentation for this one, the USB protocol documentation for the computer side says it will provide 500mA minimum, and for the device side they say draw 500mA maximum. That way manufactures know that they can draw 500mA maximum to fully power the device because they are guaranteeing that they will be given at least that amount or more. Often times ports will actually put out more because manufactures are aware that devices charge over USB, and of course you can have ports that do deliver less because of some extenuating circumstance.
Granted that is all per port (and internal USB bus is not the same as a USB hub, they often provide full power per port), if you have a hub you are using it can be less, but you can not assume its a hub.
Long story short, if it has the USB sticker on it it puts out at least 500mA all the way up to whatever the manufactures prerogative was.
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