When two or more identical capacitors (or resistors) are connected
in series across a potential difference, the potential difference divides
equally among them.
For example, if you have nine identical capacitors (or resistors) all
connected end-to-end like elephants in a circus parade, and you
connect the string to a source of 117 volts (either AC or DC), then
you will measure
(117v / 9) = 13 volts
across each unit in the string.