Now, let me get this straight ... based on what you've stated ...
(a) You neither know nor do you care what comes out of the DC-DC converters you use. You just let your employer pay for 'em, and then have the assembly guys slap 'em in there, regardless.

(b) You have a filter that costs you 11 cents, that filters out whatever the unknown noise and ripple might be, however large or small, and no matter what the frequency. How do you know that it does that? This must be a VERY clever filter design! Have you a perpetual motion machine, too, or a handy method for converting lead into gold?

(c) You do not know, nor do you measure what comes out of your filter, but you "know" that it's "good enough." How can that be?

This begs the question, "How do you know it's "good enough," or, for that matter, what "good enough" is? How can you know any of this when you don't know what's coming in? How do you know what the converter does at Vin = 32 volts or when it's at 18 volts? What happens when the input goes from one to the other, particularly when it does that for only a millisecond or two?

What? You don't believe that it varies? How do you know that?


Well, have you ever examined that? It's not evident in what you've said so far.

Analysis has to come before design, you know. If you don't perform analysis, then what you do is not design. It's just guesswork. Surely you don't try to get by with that.