Stuart Beavon's goal for Wycombe came between strikes from Charlton's Yann Kermorgant and Dale Stephens to secure the Addicks victory.
"It's a great feeling for us," said Powell.
"It was a strange game in many ways. We knew we needed a result, but it was a similar scenario to last week when we also needed a result to go for us elsewhere.
"It wouldn't be Charlton if there wasn't a bit of edginess around the place. That's just what happens here. We had a pre-pre party last week, a pre-party after this, but we'll have one hell of a party on May 5."
Powell said he did not foresee many changes to the side for next year's Championship campaign.
"I knew in the six months I had last year I needed to bring the Charlton spirit back and get that into the psyche and it's there now," he added. "Each and every player knows what's expected and they've done that. They've been a credit to this football club."
Any reproduction, publication or redistribution of this material without the written agreement of 365 Media Group is strictly forbidden.