That specific scenario won't work. There are only a limited priorities available: Solar, Primary, Secondary and Tertiary. (Unless things changed since last looking at the electric system which was some years ago)
Solar is just its own category and always has priority over everything else.
Primary might not be used by anything in vanilla, not sure
Secondary are steam engines, fusion generators, and without this mod, steam turbines.
Accumulators are tertiary. They only fulfill power needs when all else fails.
Now, if you want to achieve your goal of solar > fusion > turbines > engines, you would need an extra priority category. As is, 2 power producers would have to share a priority, like steam engines and accumulators both being tertiary.
With that said, it would be easy to just give fusion generators the same treatment as steam turbines: make those primary too. So fusion generators and steam turbines would both share primary, steam engines would be secondary, and accumulators tertiary. This leads to just a conflict between fusion and fission, but at least since 2.0 it's trivial to design a nuclear reactor that does not waste fuel by only inserting if temperature drops below a threshold so that conflict wouldn't be all that bad. If you want, i could add that as a toggleable setting to this mod?
Also, just to make sure you are aware: fusion does throttle if it's not fully needed, so you never waste fusion fuel even as it is. The main reason for making this mod was that with fission (nuclear reactors), those will in fact always run at 100% and so steam turbines not being used is wasted fuel / energy. And by prioritizing turbines that prevents steam engines to work when turbines would cover everything anyway. But yeah, as said could add this setting anyway if you want it, or otherwise it would be good to know what exactly you're trying to achieve / what the issue is that you're dealing with and want to solve with power priorities
