Device for automatic testing of power capacitors comprising - an inductor, arranged such that it forms, together with the power capacitor to be tested, a parallel or serial LC oscillating circuit, when the capacitor to be tested is connected to the device; - a first sensor arranged for monitoring acurrent or voltage signalacross the capacitor to be measured; - a second sensor arranged for monitoring acurrent or voltage across the LC oscillating circuit; - a phase detector, whose first and second inputs are connected to the outputs of the first sensor and second sensor, respectively, the phase detector being configured to detect the phase difference between the output signals of the first sensor and the second sensor and to determine the deviation of said phase difference from 90°; - an integrating amplifier and a voltage controlled oscillator, arranged such that the output of the phase detector is supplied via the integrating amplifier to the control input of the voltage-controlled oscillator, the voltage-controlled oscillator being configured to tune the frequency of its output signal to the resonance frequency of the LC oscillating circuit based on the determined phase deviation; - a regulating amplifier, whose input is connected to a second output of the first sensor; - a power amplifier and an adjustable attenuating element, wherein the signal input of the adjustable attenuating element is connected to the output of the voltage-controlled oscillator and - wherein the control input of the adjustable attenuating element is connected to the output of the regulating amplifier for setting the power level of the signal applied via the power amplifier to the LC oscillating circuit such that it remains at a reference value; said device being arranged such that the reactance of the inductor at the resonance frequency of the LC oscillating circuit matches the reactance of the capacitor to be tested. - an inductor, arranged such that it forms, together with the power capacitor to be tested, a parallel or serial LC oscillating circuit, when the capacitor to be tested is connected to the device; - a first sensor arranged for monitoring acurrent or voltage signalacross the capacitor to be measured; - a second sensor arranged for monitoring acurrent or voltage across the LC oscillating circuit; - a phase detector, whose first and second inputs are connected to the outputs of the first sensor and second sensor, respectively, the phase detector being configured to detect the phase difference between the output signals of the first sensor and the second sensor and to determine the deviation of said phase difference from 90°; - an integrating amplifier and a voltage controlled oscillator, arranged such that the output of the phase detector is supplied via the integrating amplifier to the control input of the voltage-controlled oscillator, the voltage-controlled oscillator being configured to tune the frequency of its output signal to the resonance frequency of the LC oscillating circuit based on the determined phase deviation; - a regulating amplifier, whose input is connected to a second output of the first sensor; - a power amplifier and an adjustable attenuating element, wherein the signal input of the adjustable attenuating element is connected to the output of the voltage-controlled oscillator and - wherein the control input of the adjustable attenuating element is connected to the output of the regulating amplifier for setting the power level of the signal applied via the power amplifier to the LC oscillating circuit such that it remains at a reference value;