What's the role of capacitors in this circuit?
What's the role of the capacitors?

The two 470 pF are in series across the line so, ignoring the 47 pF capacitor, the two 470 pF act together as a single capacitor of value of 235 pF. This is commonly used and, it ensures that any RF pickup on the cable that might otherwise feed into the transformer (as a differential signal) is largely &quot;shorted&quot; to both lines.
In other words, any slightly imbalanced common-mode RF pick up is reduced differentially and both inputs to the transformer only receive a fraction of the differential RF noise that would be passed to the transformer output should the two capacitors be not present.
That's what the two 470 pF capacitors do. That much is clear.
The added 47 pF capacitor degrades the ability of the two 470 pF capacitors to reduce differential noise because, any slight tolerance difference between the two 470 pF means that the 47 pF WILL create a differential RF signal from a true common mode RF signal.
So, my belief is that the 47 pF could be an error of judgement on the designer's part but, without knowledge of the designer's intent, this is just a guess.
Another guess - the prevailing RF common mode noise on the input side is so high that the 47 pF reduces that noise by many, many decibels. In doing so, the CM noise coupled via the transformer interwinding capacitance (from primary to secondary) is reduced by a decent amount.