Spec Sheet Preview: The PSDC24 and PSDC27 series 24VDC and 2 7VDC transformer power supplies are specifically designed to provide power for the PRO700 series intercom system. One (1) power supply is required for each system, and there is no central exchange r equired. There are three (3) models with varying outputs, depending upon the total number of masters and/or remotes on each system.