High quality small switching 'wall wart' 'wall adapter' AC to DC USB 5V 1A wall power supply. These are switch mode power supplies which mean the output is regulated to 5VDC. They take 100-240Vac 50/60Hz input and output 5VDC 1A. These will power most projects for up to 1A of current (ie. Arduino boards). It can also charge many electronic devices. The plug can be adjusted for right angle or straight connection to wall outlet. It small size of 2" x 2.25" make easy to carry around.