What are the best universities in the US for studying electrical engineering (power and energy)? ?

It's great that you know exactly what you want to do. For the specialisation that you are looking for-- power and energy, University of California - Berkeley is the best university according to the rankings [1]. Other great universities in tier-1 are Stanford, MIT, Illinois, Michigan, Carnegie Mellon, Princeton, and Cornell etc. Find the link here: best electrical engineering universities