Boards like the Raspberry Pi, BeagleBone, A13-OLinuXino-MICRO, DuinoMite-Mini etc. can be powered via USB. If you want to use these boards without tying up a USB port and/or keeping them tethered to a PC, you can use this adapter.
This adapter allows you to plug a wall power supply such as WA-VAR-US or WA-UNI with an input of 6V to 16V DC into a 2.1mm center-positive barrel jack, then it provides a regulated 5V DC output up to 2A via a USB Type-A connector so you can use a USB cable between this adapter and your board.
If you combine this adapter with the TOL-08639 USB to Barrel Plug Adapter, you can use it to provide a 5V regulated supply to any system that has a 2.1mm barrel DC power jack.