Put the DC power supply in series with the resistor box and capacitance box, and one of the multimeters to measure current. Set the capacitor to around 1 Uf. Turn on the power supply and increase the voltage while watching the current measuring meter. With DC voltage the current will rise and then slowly fall back to zero. Switch the leads from the DC supply to the Variac. Now turn up the voltage and observe the meter. This time the current will rise as you turn up the voltage. This is due to the fact that the capacitor is constantly being charged and discharged by the 60 cycle alternating line voltage.