A:Answer The ST4300PBU3 is a bus powered USB hub, which means power is drawn from the USB 3.0 port (900mA) on the computer and then divided between the ports on the hub. This reduces the power delivery to individual ports. If all the USB external hard drives attached to the ST4300PBU3 exceeds a total of a 900mA power requirement, the drives may not function correctly. If the external hard drives utilizes its own power supply and is not bus powered, the ST4300PBU3 should work. If you require a USB hub with a stand alone power adapter you can consider our ST7300USB3B. Atha, StarTech.com Support