Who had more power : George III or Donald Trump ?

Parliament could and did restrain George III, establishing him as a constitutional monarch within a system of shared power. Although he had influence, particularly in appointing ministers and in his personal support for certain policies like firm measures against the American colonies, his power was checked by Parliament's authority. The system had evolved from the preceding century's struggles to prevent an absolute monarchy, so Parliament's power was a core part of the constitution, limiting the king's ability to act alone.

Trump was granted "Supremacy" by the Supreme Court.

So, I would say Trump has more power than George III.