Gandalf and Sauron

[The Barrow-Wight]

Gandalf did not return with more power. Instead he return with the allowance to reveal his power - something he was not permitted to do as 'The Grey'. With the loss of Saruman to the good side, Gandalf had to do the work of two wizards.

Sauron's power was tied up in the Ring and 'lost' with its destruction.