for 2.5' Mobile Hard Disk Two USB male connector,One is for USB 3.0 power and data, another one for USB 2.0 power only USB 3.0 Female to Dual USB Male Extra Power Data Y Extension Cable, Length: 30cm(0.98ft) Cable Allows for power to be taken from 2 USB ports, like a PC and External hard drive. Allows you to link 1 USB device into 2 USB Ports on your PC for more power. There are times you may have an external device, such as a portable 2.5 hard drive, and a standard USB cable is not able to transfer enough power to operate the device.