Let us go down to the smallest subparticles in the universe. We arrive at the plus dots, the minus dot and the bipolar dot.
The plus and minus dots have the properties of charge, momentum, electrical energy. The bipolar dot is produced when a plus dot and a minus dot occupy the same space. In effect they exist in a well. The bipolar dots have the property of mass, energy, spin, and zero DC charge.
The entire universe is made from these three basic elements. Since mass is the product of electrical charges, the units of kilograms and coulombs are sister units and mean the same thing.
Coulombs becomes kilograms and kilograms become coulombs. If we apply electrical energy to a proton in a cyclotron we find that the electrical energy has created addition mass as per Einsteins orbital equations.
Thus electrical energy produces mechanical energy and coulombs produces kilograms.