First you charge the capacitor like so from the 5v supply. +5v -> + Cap 0v -> - Then you disconnect the capacitor and reconnect it this way:

First you charge the capacitor like so from the 5v supply. +5v -> + Cap 0v -> - Then you disconnect the capacitor and reconnect it this way: +5v ------> +5v 0v -> + --> 0v Cap - --> -5v Compared to 0v you now have -5v. Consequently you get 10v between the two extremes. The capacitor will deplete fast. So you would repeat the cycle quickly. And add some more circuitry to smooth the output.