A method of determining a measure of a total capacitance of one or more capacitive elements connected to an output of a switched mode power supply is described. The method includes generating a voltage control signal to cause an output voltage controller to sweep a voltage at the output of the switched mode power supply from an initial voltage value to a final voltage value. Sample values of a current at the output measured by a current sampler during the sweep of the output voltage are received, and an integrated current value representing a measure of the total capacitance using the received sample values is calculated.