Goalkeeper Ben Alnwick had already made three outstanding saves when Smith headed the only goal of the game in the fifth minute.
Rhoys Wiggins came closest to equalising for Charlton but his 30th-minute shot was palmed on to the post by Ipswich goalkeeper Dean Gerken.
With just two wins and seven goals at home this season, Powell knows where the problem lies.
"We haven't scored enough, that is in black and white," he said.
"We don't concede too many for a side in the bottom half but goals win games.
"You need to score, even if you just nick one that can be enough.
"You have to take the chances that come your way, then it gives you something to build on or hang on to.
"I knew they would start fast and we told the players they would. That's what has won them the game.
"In the Championship, invariably teams who get ahead take a point or three. We had warnings in those first five minutes and we could not see it through. Then it was us chasing the game.
"They defended deep and manfully. They scored from a set play then they defend for 86 minutes and go home with the win.
"I won't use playing Tuesday against Doncaster as an excuse, the players are fit enough to play Tuesday, Saturday, Tuesday."