On researching USB mini Hubs a few days ago I came across this .......
"A self-powered USB hub can be used to connect digital cameras, card readers, keyboards, mice, MP3 players, memory sticks and many other handheld USB devices. For more robust components such as external drives, printers, scanners or fax machines, an AC-powered USB hub is a better choice. Some of the AC-powered hubs come with an AC-adapter, while others have the capability, but require the separate purchase of an adapter. When shopping for a USB hub, be sure to get one that will best meet your needs."
http://www.wisegeek.com/what-is-a-usb-hub.htm