Ring Selection - At the beginning of your turn, you may choose a Ring, remove it from the Power Plant and place it on a friendly character's card. That character can use that Ring's effects as if it were a relic. When that character clears, return any Rings on its character card onto the Power Plant.

Does this mean only 1 Ring per each of my turns can be placed on a friendly character's card?

Or 1 Ring per friendly character per turn? Meaning if I have 3 characters on my force, each can have a Ring placed on its card at the beginning of my turn?

One ring per turn. Otherwise, it would say per character.