I have first hand experience with this.
I have soffit vents, ridge vents and two power vents near the top of different sections of the attic. The attic is very large, about 4900sf with a 10/12 hip roof. I built the house and designed the attic ventilation this way on purpose. The ridge venting is simply there for exterior architectural effect and backup venting purposes in case the fans quit or it is not hot enough for them to come on.
To summarize a lot of “testing” and experience with the fans on/off or in one case a broken fan on hot days I know very well how this works.
Its one of those things that, yes, there is interaction between having the ridge and power fans both but it is a small percentage. A small fact that can be easily blown out of proportion in building science discussions.
The fact is this, when you have just soffit/ridge venting it meets code but barely vents the attic. (Think about all of those hot attics you go in) When you turn on a power roof fan or two, that hot air is sucked right out!
Since heat rises, all of that really hot air gets sucked right out and the lower attic area is very warm but not hot! I even have a black roof. With good soffit venting very little air is pulled from the living space, again a small percentage.