Where does the extra voltage come from?
You need to look up RMS value and see how it relates to peak to peak... 

10VRMS is 28.28V peak-to-peak. 
Half wave rectify that gets you back to 14.14V
Drop the diode voltage gets you to about 13.3V
Average out the ripple on the cap from the 100Ohm resistor
You end up down @ 12.92V