Please notice: (1)DO not used for charging,it is used for offering more usb ports 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. Features: 1. 100% brand new and high quality 2.Hot plug & 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 ports 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 7.Thespecification of the power supply is 3.5*1.35mm, 5V 2A. Specification: Item Name:USB HUB 3.0 / 2.0 USB Ports:4,7 Cable:USB 3.0 About 605mm,USB 2.0About 400mm Size:104*35*21mm,164*35*21mm Data Transfer Rate:Upto 5Gbps/480mbps Color:Black/White Compatible: WindowsXP/Vista/7 and MAC OS 9.1 or higher Package Include: 1* USB high-speed hub