Their is no guarantee, but it would benifit to be the same type, with as close to model and spec of the other, or be at least as good a quality and timings if not better, so when you pair up hopefully they will coexist at their spd timings. And make sure the slowest memory would go in slot 1, if you do not know and it fails, swap them around.
It is best to buy of the same brand and model when running dual channel, but with the standard of quality memory is manufactured to today, this is really becoming a non-issue more and more.
