Problem while simulating EMI Filter for power lines
The easiest way to test or simulation ground noise or CM noise is with a series generator using a CM choke. We used to use an audio and RF power amp., brushed motors twisted along cables, and large inductive pulses.

But you could also use a square wave using dry NC contacts in series with power relay coil.

But you should read the standard.

You can even inject a CM 6kV lightning bolt with 30 ns rise time. Use 100 ohm series R into an ideal CM transformer as  CM.

A typ. Transformer is not as balanced as a CM choke which requires 0.1% tolerance to suppress 60dB , then the Pi filter provides the LPF breakpoint.   check the specs.  A typical iron transformer power supply attenuated 70 dB for lightning on a linear DC output with a line filter.  SMPS supplies vary widely.

Go fetch Fully Understanding CMRR in DAs, IAs, and OAs
Pete Semig
Analog Applications Engineer-Precision Linear TI site