The Neptune power supply for the base unit is a 12v 1.5 amp DC power supply. This power supply is not required to use your apex. This is only needed if you want to be able to detect power outages or keep the main apex powered when the rest of the unit has no power. (requires a UPS).
the Neptune branded power supply is available at BRS or on amazon. You can also use any power supply with those values as a minimum and a 2.1mm barrel style plug.
Hope that helps.