You need this for some external drives
Bought this to use with a Western Digital 250GB USB drive. You will need it with some USB ports, like those on a monitor.

Works great.

USB Power Adapter Y Cable
USB Power Adapter Y Cable
This is good to use as an extension for your WD USB cable as the cable provided is very short and can be used for many other things also.It can be easily transported in a case along with your hard drive so you have everything you need with you at all times.
Good value,good product.

Just what you need
Some hard disks are advertised as powered by single USB cable. Don't take it for granted. Works slower that way. Add this cable and power your HD.

Returned, Did not need
This product was bought to power our Western Digital Passport Storage Devices. We discovered that our laptop has enough power through one usb port, so we did not need it. We returned it to Amazon and was promptly refunded the amount of the purchase.

USB cable worth having
Even the portable drives I use may work fine from a standard cable, it's worth having this Y cable for when other drives need more power. I'll never be caught lacking of power for portable drives with my laptop. Good insurance.