I have been given a little speaker system that claims to use a 5v, 600mA supply from a usb. Is this likely to harm or overload my machine?
Any advice greatly appreciated.
No problem at all with a USB 3.0 socket (which provides up to 900mA).
600mA is theoretically above the power rating for a USB 2.0 socket though (which is 500mA) but I suspect that thousands of people plug such amplified speakers into USB 2.0 sockets without any problems. (Unless the volume is turned up to maximum they'll probably actually draw less than 500mA anyway).