Power supply devices for generating at least one electric high-frequency power signal for a plasma having at least a first plasma state and a second plasma state are provided. The power supply devices are configured to determine a first variable that characterizes a power reflected by the plasma in the first plasma state, determine a second variable that characterizes a power reflected by the plasma in the second plasma state, generate a third variable based on the first variable and the second variable, and control at least one of a frequency or a power of the high-frequency power signal based on the third variable.