An electrosurgical generator having connectors for an electrosurgical instrument including a high-voltage generator electrically connected to the connectors and produces a high-frequency alternating current in its activated state and output said high-frequency alternating current via the connectors. The electrosurgical generator has an effective power determination unit including a phase shift determination unit that supplies an output signal representing a phase shift between the current and the voltage of an alternating current output during operation. The phase shift determination unit produces a pulsed DC voltage signal, in which the pulse width reflects a time difference between the zero crossings of the current and the voltage—；and consequently the phase shift—；and to process the pulsed DC voltage signal by way of a low-pass filter to form a low-pass filter output signal, the magnitude of which depends on the pulse width of the pulses of the pulsed DC voltage signal.
