In numerous applications, drive and control systems with a direct mains connection were almost completely replaced by external auxiliary power supplies. Supply to the application is with a protective low voltage; there is no direct connection to the mains power supply. Depending on the technical concept of the drive system, the power supply is with DC or AC. To ensure that the different voltage types cannot be confused – this could destroy the drive system – DEWERT auxiliary power supplies are fitted with a connector system which provides protection against incorrect connection. Auxiliary transformer: The unit delivers alternating current; the rectification needed for the necessary DC drives is fitted in the control unit. Auxiliary mains unit: The unit delivers direct current. Thanks to its greater flexibility when compared with the auxiliary transformer, DC voltage supplies are becoming increasingly important.