A few days ago, I was in the lab doing some experiments with capacitors and something weird happened... I connected the capacitor to a DC power supply and after a few seconds the capacitor has popped. The voltage applied to it was within its working voltage, so that was not the cause. My lecturer then told me that I connected the leads to the capacitor the other way round and he was right. Then I asked him the following question in which he was unable to answer it... If I have a DC power supply and connect the leads to the capacitor in the wrong way, it will pop! This means that the current is only allowed to flow in one direction... So why don't they pop with an AC power supply?