The problem with "dirty" power supplies
Ideally, your power supply will have zero noise; but in the real world there will be noise.

Practically speaking, for a one off project you should just try it out and see if it causes problems.

For systems that need to be very reliable, it may make sense to do analysis of what the pi is specified to handle, vs what is measured from the power supply. However, even in this case the systems are too complicated to exhaustively simulate what might happen, so there's still going to be empirical testing and "best practices" involved.

If you find that there are issues, you have various options to remedy them. The simplest and most practical is to switch to a different type or model of power supply. Building a filter may also work, but it can be difficult because digital devices require quick bursts of power that the filter may interfere with. If you go this route, you'll probably want an LC low pass filter.

I've powered raspberry pi's many times using switching power supplies without additional filtering, so it's definitely possible.

TLDR; I would recommend trying it. If you have issues I would try a different power supply.