Hi Someone,
1) 12VAC has a peak voltage of 17V which is reduced 1.4V by a bridge rectifier that isn't loaded very much. Therefore the cap will be charged to at least 15.6V.
2) A 110V to 12V transformer will have an output that is higher than 12V if it isn't fully loaded.
Guillermo didn't say if he wants isolation and also didn't say how much current. A 1M resistor in series with a 1N4004 diode, feeding a 1uF cap with an 82K resistor in parallel with it will give about 12VDC output.