This 12V, 2.5A power supply is used for powering the Sun Harvester Driver Board. More specifically, it is sized to
work with the NEMA 17 Stepper Motors also sold in this store.
Since the majority of this store's customers are outside the U.S., it makes sense to provide an international power supply. This is why multiple types of plugs are provided with this purchase (pictured below). Simply choose the one that matches your outlet and you're good to go.
The end of this power supply's wire must be cut off in order to insert it into the screw terminals on the Sun Harvester Driver board or Breakout Board.
The wire with the dashed grey lines goes to M+ (positive wire). The wire with the writing on it goes to GND (negative wire). The image below shows an example.