DC motor voltage (current load of 280mA) from a 50Hz power supply employing first a 2.2 mF electrolytic smoothing capacitor, and then replacing it by a 3 F, 2.7 V PowerStor supercapacitor (see circuit in inset), before and after the interruption of power supply (0 to 75 s). Ripple voltage is shown in the inset for the PowerStor supercapacitor. From 75 s onwards, the power is restored and the startup times for both devices are compared. See [Anis Allagui; Ahmed S Elwakil; Mohammed E Fouda; Ahmed G Radwan. Capacitive behavior and stored energy in supercapacitors at power line frequencies. Journal of Power Sources, 390 , pp. 142–147, 2018] for more detail.