Transformer power rating and RMS current?
LTSpice is telling you that a 13.5 volt peak amplitude sinewave has an RMS value of 

$$\dfrac{13.5}{\sqrt2}$$ 

This is 9.5 volts RMS.

It's also telling you that the RMS current it supplies into the bridge is 1.96 amps but, the power delivered to the bridge and its output is only 12.36 watts.

This however doesn't mean that RMS current x RMS volts = watts. The bridge and reservoir capacitor is a highly non-linear circuit and the true power delivered is 12.36 watts but at a VA of 18.6 volt-amps.

Transformers are rated in VA and not watts.