(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 speed1.Thespecification of the power supply is 3.5*1.35mm, 5V 2A.2.Hot & play USB device3. Fully compatible with USB specification version 3.04.With blue LED for power5. 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 needsItem Name:USB HUB 3.0USB:4Cable:USB 3.0 About 605mmSize:104*35*21mmData Transfer Rate:Upto 5Gbps/480mbpsCompatible: WindowsXP/Vista/7 and MAC OS 9.1 or higherNote: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