A lacklustre first-half display from Charlton allowed Ipswich to build a 2-0 lead with goals from DJ Campbell Daryl Murphy.
Powell's team fought back in the second period but could only pull back one goal and the Charlton boss hopes they can turn their form around quickly.
"I'm not enamoured with what happened, especially first period," said Powell after his 100th game in charge at the Valley.
"We were duly punished. It doesn't matter if it is against a team in the lower reaches, or any team. If you are not at your full capability you will get punished and that is what happened in the first 45.
"It shows how quickly things can change in the Championship.
"We went on a superb run but now we have lost three in a row. We have been here before and have responded and we have to do that again."
Powell added: "No excuses. We were beaten by a better team, especially in the first half.
"We were very loose and sluggish in our marking. Ipswich didn't have chance in the second period but the damage was already done
"We were huffing and puffing and put players on, but you need a platform to perform and we were very up and down."