Bradley Wright-Phillips saw a second-half penalty saved by Stuart Nelson after Neal Bishop had put the hosts ahead shortly after the break, but Powell did not think the keeper should have still been on the pitch.
In the first half, the Magpies custodian bundled Joe Anyinsah over after the ball had gone, but was only booked.
"You would think it would be red, because I don't think there was a covering defender, but the referee made his decision," said Powell.
"Those small moments change games and if you want to move up you have to take them.
"The home team were on the front foot but we did have a few chances."