RC differentiator giving a higher output amplitude than input amplitude
It's called "charge pumping", and it is sometimes used to create low-power boosted-voltage supplies for some applications.

At the end of each half-cycle, the capacitor is essentially charged to the same voltage as the source. When the next half-cycle starts, this voltage cannot change instantaneously, so the capacitor voltage is added (in series) to the source voltage. But this quickly discharges through the resistor, and by the end of that half-cycle, the capacitor is charged in the other direction.