Steven Gillespie had the ball in the Addicks net but it was eventually chalked off after the referee consulted his assistant, leaving Bradley Wright-Phillips to settle the match with a 78th-minute winner - his first goal as a Charlton player.
Powell, who celebrated his second victory in as many games since taking the helm at the Valley, said: "Football is a game of emotions. We all get excited and upset.
"You just hoped our boys kept their calm and they defended like Trojans. We cleared one off the line. It was tough but we dealt with it.
"It was a patchy performance. The first half wasn't the way we'd like it but in games like that you have to keep your calm and go in at half-time without conceding. There were a few choices word and we improved in the second half.
"We still had that belief it would come and Bradley came up with his bit of magic. We're a work in progress but for me, two home wins and two clean sheets is a decent start. If you know you're not going to concede you know you've got a chance."
Source: PA
Source: PA