essentially all ad systems use some form of a “if a user watches an ad, you get a little money” often with a bonus if they click through. so while you may think by adding more ad systems you would get more, but in fact you would only get more, if the second one pays out better.
say one system gives you $0.003 per ad viewed, if you then add a system that gives $0.002 per view you would be loosing $0.001 for each ad in the new system.
what you should do is see how much you get per ad viewed or how ever it’s measured, and use the one that you get the most from. however if one is showing ads for catering and the other for games, the one with games will get more click through bonus while the one showing catering ads wont.