This is a high quality 'wall wart' AC to DC 5V 2000mA Barrel Jack wall power supply. These are switch mode power supplies which mean the output is regulated to 5V and the capable output current is much higher（2000mA）.
These wall adapters are perfect for supplying power to many single-board computers with a barrel jack. Please note, this specific supply（5V/2A）is also FCC/CE certified and works with 100-240VAC inputs and has a Center-positive 5.5x2.1mm barrel connector.
