Behold, the Hydra! This USB power cable probably looks a lot like something you've hacked together before. We do it all the time, because what is a computer if not a 5V power supply that happens to run software?
The Hydra brings the 5V and GND lines from your USB power supply, computer or otherwise, and breaks those lines out into three common power connectors: Barrel Plug, JST and Alligator Clips! The clips are shrouded to avoid shorts and the barrel plug is center positive. The cable is 6 feet long overall which give you plenty of room to work.
Remember that USB power does have its limitations. Most USB hosts will only provide between 100 and 500mA at 5VDC.