"Fair"; A reward equally pleasing to the rewarded and the rewarder and what the rewarder would seek for the same action.
"Justice"; The appropriate compensation for actions.
"Power"; The driving force or strength to perform an action.
Most of today's dictionary definitions for those terms are so vague I've chosen to provide my own which are all woven into each other. By those definitions they are what every individual should ask themselves before preforming any act. They are very difficult to translate to a system of external control especially during these times of selfish greed and superior mindedness usually taken by people allowed a position of authority over another which began with parenting.
To translate that information to a system of governing a group of people as in home, school, church, city, state and nation people with the "power of governing" are required to be selfless - meaning; they desire for everyone under their authority the same they desire for themselves - and before deciding a matter put themselves in the position they are about to make a decision concerning. In that state of mind as a leader of people their "power" would be "just" and "fair" because it is what they want for themselves.