(1)DO not used for charging,it is used for offering more usb to transfer file. (2) The power supply can solve the problem of insufficient power supply, if you need work with a hard disk , then you should choose the with power supply , and please note ,please don't use more than 2 hard disk at the same time (3) The power supply can improve the usb transmission speed 1.Thespecification of the power supply is 3.5*1.35mm, 5V 2A. 2.Hot & play USB device 3. Fully compatible with USB specification version 3.0 4.With blue LED for power 5. ON/OFF switches activate or deactivate individual 6.Designed with 4-port,7-port,this compact USB3.0 high-speed hub is small enough for travel,and cable enough to meet your connectivity needs Item Name:USB HUB 3.0 USB:4 Cable:USB 3.0 About 605mm Size:104*35*21mm Data Transfer Rate:Upto 5Gbps/480mbps Compatible: XP/Vista/7 and OS 9.1 or higher Note: Due to the different monitor and light effect, the actual color of the item might be slightly different from the color showed on the pictures. Thank you! Please allow 1-3cm measuring deviation due to manual measurement. Package Included:1 x USB Hub