you can use the 24V model to power 24V DC pumps. If you approach the maximum current it is able to provide at 24V, it will drop the voltage so that it is able to maintain its rated current. This voltage drop is harmless to Jebao pumps, that is how some people adjust their power.
I don't know what you could do with the 42V version, unless you have a 42V DC pump (you don't).