what is the difference between PI filter and Common mode choke with X2 capacitors?

Thread Starter

Younes Thabet

Joined Jan 9, 2019
I have noticed that a PI filter can be both before and after a bridge rectifier. when placed after, it help to produce a very low ripple smooth DC output (like in image below)
Also I have seen multiple PSU with a common mode choke and X2 capacitors forming a PI filter (as in below image), I am guessing to act as both low pass filter and common mode suppressor.

So is this considered as a PI filter (before bridge) or it is something totally different?
Plus how can i calculate right capacitor and inductor values in both cases?