Understanding a voltage multiplier circuit
It's called "voltage doubler".

During the positive half cycle D1 conducts and charges C1 to peak value of the input voltage minus one diode drop. Likewise, during the negative half cycle D2 conducts and C2 gets charged to peak value of the input voltage minus one diode drop. Since C1 and C2 are connected in series, the output voltage will be the sum of the voltages across both capacitors: Vo=2 (Vin-pk - Vf) = 2 × (1.414 × 5 - 0.6) = 12.9V. Depending on the load current, the output voltage may drop due to the output ripple.