I have seen quite a few offline SMPS schematics with 100pF or so capacitors across the diff mode filter inductors. This is said to offer the opportunity to shift peaks in the EMC scan to different frequencies where they may be under the limit line of the conducted EMC test.
I believe that this is not applicable for offline SMPS, and the only thing that should go across the diff mode inductors is damping resistors, would you agree?
Also, would you agree that the switching frequency of an offline SMPS should never be at the SRF of any of the filter inductors in the AC filter section?...This only really applies to common mode chokes, because for diff mode inductors the SRF is usually well above the switching frequency anyway.
So would you agree that one of the major considerations for a common mode choke selection in an offline SMPS , is where is the diff mode SRF?