Add a power switch to any project simply by plugging this between the power supply. This is the most useful thing you never knew you needed! You'll want to pick up a bunch for your electronic projects.
Comes with a 5.5/2.1mm barrel jack on one end an a plug on the other. In between is an in-line switch that is rated for 125V and 2Amps (its normally used for lamps, they suppose). Since most people will be using it with no more than 12VDC, they think it can probably handle up to 5A at that voltage.