Folks new to the Neo Geo often find it difficult to figure out which power supply is appropriate for the particular version of the Neo Geo home system that they have.  There are several different versions...

PRO-POW
power input AC100V 
power output DC5V 3A

PRO-POW-UL
power input AC120V
power output DC5V 3A

PRO-POW2
power in AC100V 
power out DC5V 3A

PRO-POW3
power in AC100V 
power out DC10V or DC11V

If your power in is AC100V then you've got a Japanese system. US Systems power input is AC120.