Tubed-amp power-supply question

Do we have any audio EEs here?

In a ‘pi’ filter with 2 caps connected by a choke, I’ve seen amps with some hi-quality (‘propylene and ‘styrene) capacitance in parallel with the choke. What’s the purpose of that?
A cap in parallel with a choke creates a notch filter, one that is tuned to and has a very high impedance to a narrow range of frequencies. By choosing values that produce a filter centered at the ripple frequency of the power supply, usually 60 or 120Hz in the US, the ripple voltage that passes through is reduced.
Awesome answer!
Awesome indeed. TYVM.