On Apr 30, 2012, at 9:39 AM, Henk Gooijen wrote: Well. The max from a port is supposed to be 500 mA at 5v (so 2.5W). That's what you'll get from a standard port on a powered hub. Some hub-like devices (e.g. unpowered hubs in keyboards, etc.) siphon off some of that power for themselves, and have to divide it between multiple ports, so they have somewhat more stringent limits. Most USB wall adaptors will supply up to an amp, and there is a "Hi Power USB" or somesuch used to attach external drives to laptops, but that has an augmented plug that you'd notice. As far as a device that provides a simple indication, I suppose you could always slice up an extender cable and put an ammeter in series with the +5v line. The USB device itself is supposed to say how much current it expects to use; on OS X, you can see that value in the System Profiler, but I think whatever the USB equivalent for lspci (is it lsusb?) will do it on most common Unix-ish systems. Devices, of course, can lie about how much power they want to use. There's not really a lot of enforcement aside from circuit breakers which cut off gross overcurrent, and some implementations don't even have them (they'll let a short bridge +5v to GND without so much as a resistor in the way, inasmuch as your superheated cable is not a resistor). - Dave