The Addicks have thrown away leads to lose 2-1 in their last two matches, and Powell has called on his players to find their shooting boots.
"Palace couldn't really handle Ricardo Fuller and the way we broke from midfield, but you do need to take chances, even at this level," Powell told reporters.
"We talk about the Premier League and one chance and it is in the back of the net, but even at Championship level you do need to take the chances that arise and the chances that you make. We didn't do that."
Charlton currently sit 14th in the Championship table.