An apparatus for supplying power to an illuminant can be configured for use for different illuminants, a configuration can be chosen by a resistor on a secondary side of the apparatus. A primary side has at least one switch and a control device. The control device is set up to bring about clocked switching of the at least one switch in an operating phase in order to take a measured variable captured during the operating phase on the primary side, the measured variable is dependent on the resistor, as a basis for identifying a configuration stipulated by the resistor. The control device is set up in order to control the apparatus in a further operating phase on the basis of the identified stipulated configuration. A method for controlling the apparatus is also provided.