This is a high quality AC to DC 'wall wart' which produces a regulated output of 12VDC at up to 600mA. These are switch mode power supplies which means the output is regulated to 12V（no more 14V outputs）, and the capable output current is much higher（600mA）.
These will power most projects that don't require more than 600mA of current. This wall wart has a center-positive 5.5x2.1mm barrel connector and works with 100-240VAC inputs.
