What governing factors determine how loads are powered?

It isn't power that is being shipped it is the forced motion of electrons being manipulated to do something useful.

The governing factors are: voltage(V), current(I) and resistance(R).

Source A has a voltage potential. Once connected to said motor, which has a certain amount of resistance it will permit a certain amount of current to flow through. Specifically V/R = I ( ohms law ). It's the current ( flow of electrons) as a result of potential difference on a conductive wire that allows that "power to be shipped". I hope i understood your question correctly

 

I don't know what power source you're referring to that can do such a thing. A battery for instance does not determine anything, it provides a potential difference. Lets say for instance we have a 300 hp motor with a resistance of R, just because i hook it up to an electric power source doesn't mean it will dissipate 300 hp. Horse power is related to wattage by 1 hp = 746 watts. Electric power in wattage is calculated by voltage*current. So if i wanted to know what potential to run across this motor to achieve its 300 hp rating :

746*300 gives us its power consumption of 223800 watts
223800/R = would tell us the voltage required run the motor with 300 hp.

I think you're using the terms energy and power a little too loosely. In physics and electrical engineering they are related but are not one and the same.