These printers use a thermal head to heat the special receipt paper and draw images and text. That makes the printer very small — there's no moving ink head — but it means they require a lot of power. This printer in particular requires 5 to 9 Volts, 1.5 Amps current! That means you will need a fairly beefy supply and you cannot run it off of USB power. An external adapter is required!
We suggest using the 5V 2A power supply in our shop. It’s got plenty of power to keep the printer happy and you can also use it to run some microcontrollers or sensors off of the remaining 500 mA current that is not required by the printer.
A quick way to power the printer is by just using a 2.1mm jack adapter, which you can attach to the printer’s red/black wires: