Circuit arrangement via which a voltage type and value of an input voltage of a power supply or a switching-mode power supply is ascertained is configured such that the input voltage of the power supply decreases at the input side and includes a differential amplifier for converting the input voltage into a signal rectified by a first rectifier such that a forward voltage of the first rectifier is compensated, includes an inverter which generates an inverted signal rectified by a second rectifier such that a forward voltage of the second rectifier is compensated, includes a mixer via which a first output signal is generated from the useful signals, from which first output signal a second output signal is derived via a filter such that the voltage type is determinable from the first output signal, and a voltage value of the input voltage can be determined from the second output signal.