Capacitors As Temporary Power Sources - FIGnition FUZE Hardware Reference Manual

So, if we were to draw a graph of the voltage over time across the capacitor it would look
like the graph on the left:
! ! !
And a graph of current over time would look like the one on the right:
C.2 Capacitors As Temporary Power Sources
If the power source dips below 5v then the reservoir of electrical charge on the left plate
floods back into the left hand part of the circuit replenishing it with charge, but not for long
because the plate stores relatively little charge (compared with the power source).
And this will cause a brief negative current flow across the capacitor: