Yann Kermorgant scored twice, while Jonathan Obika and Johnnie Jackson got on the scoresheet to ensure the Addicks ended the campaign ninth and undefeated in eight games.
"It was a terrific end for us and we did it the right way," Powell said.
"Seasons have tended to tail off for us and I wasn't going to allow it this time, especially at home.
"We have shown we can play in this league and I am a better manager for it and the players are better for the experience.
"This club has always battled against the odds and, when we started the season, everyone expected us to be in the bottom six, especially as we have one of the lowest budgets in the division.
"But the supporters believe in the club and in the players. It is not about me because when I am long gone they will still support in the same way.
"There are no boundaries as far as they are concerned and I think we have done them proud and it was fitting to put on a show."