Powell accused Grand Final referee Ben Thaler of losing his cool after his side suffered a 33-26 defeat by Wigan Warriors last month.
Powell, who spoke out in the post-match press conference, has been fined £500 and warned as to his future conduct after being found guilty of improper conduct.
Half the fine is suspended until the end of the 2017 season and Powell has 14 days in which to submit any appeal.
Paul Anderson (Huddersfield) and Denis Betts (Widnes) have also been fined this season for publicly criticising a referee.
Salford have been ordered to appear in front of Rugby Football League tribunal to answer a charge of misconduct.
The Red Devils have been charged with breaching RFL operational rules following a crowd disturbance at the end of their 26-24 win at Huddersfield on Easter Monday.
Salford players Justin Carney and Junior Sa’u entered the crowd after the final whistle to protect their families caught up in fighting among the Salford fans and police were called.