[Piotrsko]

With capacitors, the voltage is determined by physical spacing using the dielectric material as the spacer. Better spacer insulation gives you more capacitance because the plates get closer together. However, at some point the plates get so close together that the current flows from one edge to the other. Aka breakdown voltage, aptly named. Caps in series will cascade failure because a larger voltage applied pretty much guarantees sequential failure.

Generally, unless you have some filter scheme that requires frequency taps, Caps shouldn't be used in series

Back in the day, you could "stack" them and be sucessful because the working voltage generally exceeded the signal voltage by a dosen factors and all you had were large value caps in your storage. You used parallel resistance charts and solved for the required values.

You CAN get large value caps at higher voltages but they have to be larger. I have seen a 100 mfd cap for line voltage that was the size of the power transformer on your light pole outside the neighborhood