I got this 4 port usb hub, but it's unable to power all my devices connected to it. It currently has a printer, ext 3.5" hd, int. 2.5" hd and a Logitech MX Revolution mouse adapter on it. The only thing that works properly is the 3.5" ext. I can't use the mouse adapter to its full functions, can't print in normal speed or access the 2.5" int hd. I know this is due to the lack of available power on the hub. The hub does have a hole for power, but I don't know which power adapter I should be buying for it (in terms of voltage and amperage). What I do know is, a USB port has 500 mA of power on tap while the USB hub itself requires 100 mA leaving 400 mA. I just don't know which power adapter to get.