If you're calculating the power of an athlete who is lifting weights, or the power of a windmill that is pumping water from a well, or the power of two horses turning millstones, then those electrical units won't help at all.
But if you happen to be calculating the power delivered to an electrical circuit or dissipated by an electrical device, then you can use ...
(voltage) times (current) or (voltage)² divided by (resistance) or (current)² times (resistance) .
The choice just depends on which quantities you know or can easily measure.
