An electrical system having, among other things, a resonant DC-DC voltage converter with two resonant capacitors, a control unit having a first module for determining a maximum value and a minimum value of the voltage at the terminals of each resonant capacitor as a function of an output voltage of the converter, a module for comparing between the maximum value and respectively a minimum value of the voltage at the terminals of each resonant capacitor and a failure detection element configured to detect a failure of the converter if the maximum value is greater than or equal to the upper voltage limit, or the minimum value is less than or equal to the lower voltage limit.