Designing an electronic product for the american market, need to find a DC to DC converter with FCC certification
In round numbers, FCC cert applies to the finished product.  Although many switching power supplies come with FCC cert to Class A or B, this does not guarantee that a finished product will meet the rules because of radiated or conducted noise coming from other devices within the product.

The basics are that you build a prototype and send it to a certified testing lab.  The lab does the tests and gives you a report telling you where it passed and where it failed.

https://en.wikipedia.org/wiki/FCC_Declaration_of_Conformity

https://en.wikipedia.org/wiki/Title_47_CFR_Part_15