Algodoo

TLDR: Click on the red shape 1 or 2 times and see what happens.

Capacitors can be used to smooth an incoming pulsating Direct Current (DC).
This simulates the current as flow of water. Voltage as height (water pressure).

State 1: No capacitor - The current flows just from the supply (full bridge rectifier simulated as the wheel)
State 2: Small capacitor, high conductivity - Click on the red L-Shape and a "capacitor" appears. The current is only partly smoothed since the capacitor fully discharges.
State 3: Big capacitor, low conductivity - Click again.