Common mode inductor and diode circuit (EMC filter?)
The main purpose is to measure the input current (i.e. the current drawn from the source).
T101 is a current transformer. When the input current (a switching current) flows through T101's primary, a non-zero current proportional to the input current (and, in-phase of course - look at the dots) flows through the secondary:
$$
n=\frac{N_p}{N_s}=\frac{V_p}{V_s}\\
V_p\ I_p=V_s\ I_s\\
\therefore \frac{I_s}{I_p}=n
$$
So, for example, for 1A primary current the secondary current can be 1mA.
The output current is then rectified via CR100. And this current drops a non-zero voltage across the burden resistors (R101 and R102. These two resistors also act as a voltage divider). This voltage is fed to the measurement circuit (analog or ADC) through an RC filter formed by R202-C102 pair.
One advantage of this circuit is that the measurement can be done with respect to any reference since the output current is isolated.