A little bit off topic from the OP's question, but since people are trying to define what "rated voltage" means...
Rated voltage for a capacitor is more complicated than "more than rated and it dies." You need to also consider "when." The rated voltage gives some measure of how thick the dielectric layer is, which varies significantly by dielectric.
In all cases, the dielectric's thickness is such that the "rated" voltage allows the part to pass some qualification / life test. Typically it is 1000 hours with less than 0.1% of the parts failing. Sometimes this means a thicker dielectric, other times, it means reducing the requirements of the life test.
For example on X7R ceramics it is common to run the lifetest at 1000-hrs, 2X rated voltage, 125C. While X5R will be run at rated-voltage, 85C. This means the X5R can be thinner since it doesn't have to survive such harsh requirements. You could also imply the X7R dielectric layer more robust than the X5R.