I wish to know is why the multimeter is showing 40V for just 30V rms value. Could someone shed light on the theory behind c shunt filters. I have attached an image for the same. It is a mulisim simulation.

 

The rectifier stores the peak voltage of the input in the capacitor. The input is 30V rms which has a peak of 1.4142 times the rms value.

 

okay. What is the solution to get a pure dc of 30V for the same configuration with minimal current loss?

 

Use a 23V transformer.
Or use your present circuit with a 30V regulator.

 

I get something like: =1.41*(30-1.4)
The 1.4 is two diode drops going through the bridge rectifier. The 1.414 is the sqrt(2) to convert to the peak value.

40.326

See what the SIM is calculating for the diode drops.