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Electrolytic capacitors.

If there is nowhere much for the electricity to go, that will be very soon, like if you tried to send lots of cars down a short cul-de-sac. But you can make life easier for the electricity if you give it room to spread out, like if there were a large car park at the end of the cul-de-sac. And when you stop pushing the electricity in, it'll all come piling out again as soon as the pressure is released.