I didn't mean to question you or state the obvious. But then I started thinking, just because it's obvious to me (I have a degree in EE) does not mean it's obvious to the population at large. I just wanted to make sure that since you are volunteering your time to conduct an experiment that we will all benefit from, you would not be wasting your time (in case you didn't know that the load will limit the current the source puts out).

With two power banks at 2.0 amps each you can test for the max 4.0 amp output from the panel (I'm assuming you have two ammeters). Just barely, it would be better if you had power banks that could accept even more current. But I'm assuming you only have two power banks and your power bank only has two outlets. If you had three power banks and three outlets, you could easily test for 4.0 amps max output! But you can't test if a single outlet can reach its advertised 2.4 amps. I guess you could use a USB hub to try and charge two power banks from a single solar panel USB output. I'm not even sure it that would work - I've never researched the internals of a non-powered USB hub, and it may limit current as well.