Most of the USB external hard drives that I have seen are of two types. 2.5 drives that draw power from the usb port or 3.5 drives that have an external power supply. If the power connector does not look like a standard PC case type then you are missing the entire external power block and not just a power cable. If that is the case then going to the manufacturer's web site is your only hope. I have three external drives, one 2.5 and two 3.5's from different vendors oh and a fourth 1.8 inch 40 gig SOYO pocket drive.