A power supply module (22; 22') for a public lighting installation, said power supply module having Class II electrical insulation, said power supply module comprising: - input terminals (32, 34; 32', 34') configured to be connected to a phase conductor and a neutral conductor coming from a power supply station connected to a first electrical earth point; output terminals (46, 48; 46', 48') configured to be connected to a lighting module; - an AC/DC voltage and current converter (38, 44; 44'), connected between the input terminals and the output terminals of the power supply module, defining a galvanically isolated primary circuit and a galvanically isolated secondary circuit; and - a filter capacitor (C1; C1') connected between a point referenced to the primary circuit of the converter and a point referenced to the secondary circuit of the converter, class II electrical isolation of the power supply module means that the power supply module has no direct electrical connection to earth and has galvanic isolation between its primary and secondary circuits, characterised in that the power supply module (22; 22') further comprises: - a detection circuit (54; 54'); and - a counter connected to the output terminals (70, 71) of the detection circuit, the detection circuit comprising: - a sensor configured to: ∘ measure an electric current (Isurge) flowing, in the event of a common mode overvoltage (Usurge) between active power supply conductors (28, 30) of the power supply module and a local reference earth of the power supply module, in an arm (52; 52') of the power supply module comprising the filter capacitor (C1; C1'); and ∘ deliver a measurement voltage (Usense) representative of the measured current, - a processing stage configured to supply, in the event of overvoltage, a rectified electrical voltage signal at the output of the detection circuit based on the measurement voltage; the detection circuit thus being configured to detect a common mode overvoltage (Usurge), the counter being configured to count the number of common mode overvoltage events based on the output voltage signal of the detection circuit. - input terminals (32, 34; 32', 34') configured to be connected to a phase conductor and a neutral conductor coming from a power supply station connected to a first electrical earth point; output terminals (46, 48; 46', 48') configured to be connected to a lighting module; - an AC/DC voltage and current converter (38, 44; 44'), connected between the input terminals and the output terminals of the power supply module, defining a galvanically isolated primary circuit and a galvanically isolated secondary circuit; and - a filter capacitor (C1; C1') connected between a point referenced to the primary circuit of the converter and a point referenced to the secondary circuit of the converter, class II electrical isolation of the power supply module means that the power supply module has no direct electrical connection to earth and has galvanic isolation between its primary and secondary circuits, characterised in that the power supply module (22; 22') further comprises: - a detection circuit (54; 54'); and - a counter connected to the output terminals (70, 71) of the detection circuit, the detection circuit comprising: - a sensor configured to: ∘ measure an electric current (Isurge) flowing, in the event of a common mode overvoltage (Usurge) between active power supply conductors (28, 30) of the power supply module and a local reference earth of the power supply module, in an arm (52; 52') of the power supply module comprising the filter capacitor (C1; C1'); and ∘ deliver a measurement voltage (Usense) representative of the measured current, - a processing stage configured to supply, in the event of overvoltage, a rectified electrical voltage signal at the output of the detection circuit based on the measurement voltage; the detection circuit thus being configured to detect a common mode overvoltage (Usurge), the counter being configured to count the number of common mode overvoltage events based on the output voltage signal of the detection circuit. - a detection circuit (54; 54'); and - a counter connected to the output terminals (70, 71) of the detection circuit, the detection circuit comprising: - a sensor configured to: ∘ measure an electric current (Isurge) flowing, in the event of a common mode overvoltage (Usurge) between active power supply conductors (28, 30) of the power supply module and a local reference earth of the power supply module, in an arm (52; 52') of the power supply module comprising the filter capacitor (C1; C1'); and ∘ deliver a measurement voltage (Usense) representative of the measured current, - a processing stage configured to supply, in the event of overvoltage, a rectified electrical voltage signal at the output of the detection circuit based on the measurement voltage; the detection circuit thus being configured to detect a common mode overvoltage (Usurge), the counter being configured to count the number of common mode overvoltage events based on the output voltage signal of the detection circuit. ∘ measure an electric current (Isurge) flowing, in the event of a common mode overvoltage (Usurge) between active power supply conductors (28, 30) of the power supply module and a local reference earth of the power supply module, in an arm (52; 52') of the power supply module comprising the filter capacitor (C1; C1'); and ∘ deliver a measurement voltage (Usense) representative of the measured current, - a processing stage configured to supply, in the event of overvoltage, a rectified electrical voltage signal at the output of the detection circuit based on the measurement voltage;