There is a list of tested compatible RAM sticks for every MB (QVL), http://www.asrock.com/MB/AMD/X370%20Killer%20SLIac/index.asp#Memory
if in doubt look at that list and for other ones you can check and see if there are some with same characteristics. There's only few companies in the world that make actual memory chips and even less that make controller chips for them. Some of reasons RAM is so expensive nowadays.
Rest of other makers just use chips from those few manufacturers o put together and sell actual memory sticks.