The goal by the Tottenham loanee rounded off a good week for the home side who opened the scoring through Johnnie Jackson before Luke Varney equalised for Leeds with the game heading for a draw before Obika's late intervention.
With Charlton earning seven points in a week, Powell was full of praise for his side after their first stoppage-time goal this season.
"I'm really pleased with the whole week, ecstatic with the performance today - we didn't deserve to be at 1-1," he said.
"It has been a pivotal week, to get seven points and a real gritty, dogged point at Brighton. We have to do these things to survive in the Championship. And there's no better way of winning than in the last minute.
"We knew we had that tag of least home wins, but that's gone now. Our away form has kept us going, and during the international break I thought that we had four home games we could win.
"To beat Leeds was fully deserved, we have Wolves and Bristol City and we can keep carrying on. Any point in the Championship is massive - I don't want our players relaxing. I've set them no targets."
Leeds caretaker manager Neil Redfearn was disappointed with the last-minute defeat, but was pleased with the response of the players after Neil Warnock departed Elland Road in the week.
"I thought the performance and application was good, I thought we were unlucky at the finish because we should have got a couple of decisions," he said. "From a performance point of view, I thought we went a goal down against the run of play - we were doing well up to that point.
"Whenever the manager leaves, it's upsetting - these are players that Neil Warnock signed. But they've applied themselves well. I thought it was good performance without being spectacular, it was a poor surface. They will be disappointed, but they've been professional at what they've done."
- Sports & Recreation