I never said you couldn't charge a capacitor like this. I said (a) that it was a bad idea to charge a capacitor living in a portable device using a small power and (b) that it's extremely inefficient. (And (b) tends to imply (a) when the power brick is a tiny little thing with limited heat dissipation.) You also have the capacitor's leads to worry about if you scale to cell-phone-battery-sized capacitors.