Connecting capacitors in series after charging them
The electrons will not rush to equalize the charge at the connection between the two capacitors, because the charges are held in place by the counter charge on their respective opposing plates.
Similarly there is no explosion or short when you connect multiple batteries in series in order to multiply the voltage, eg. obtain 6V from 4 AA 1.5V batteries.
There are concerns, however, when connecting capacitors in parallel when their voltages are not equal. In that case an equalizing current will flow, and its magnitude is only limited by the (small) resistance of the interconnecting conductor (wire).
There are grave safety concerns when electrolytic capacitors are connected with reverse polarity, so when attempting any of the above, polarity matters even with small voltages.
As an interesting aside, a &quot;voltage multiplier&quot; works on the principle of charging capacitors and then connecting them in series in order to obtain a higher voltage than the supply.
https://en.wikipedia.org/wiki/Voltage_multiplier