A power supply unit, preferably for a power analyzer, a power analyzer comprising a power supply unit and a method for operating a power supply unit, wherein the power supply unit comprises a feedback control unit controlling the output level of the voltage, the current or the power supplied to output terminals of the power supply unit on a preset value, means for sensing the actual output level of the voltage, the current or the power, respectively, and sending a signal representing the sensed output level to said feedback control unit, and means for detecting oscillations in the actual output of the voltage, the current or the power, respectively and for issuing an oscillation detection signal to the feedback control unit, wherein the feedback control unit is arranged to adapt at least one parameter value of the feedback control in response to a value of the oscillation detection signal.