Max Jowitt split the posts with two penalties and added the extras to his own try as Wakefield punished an error-strewn first-half performance from Hull to take charge of the Super League contest on Thursday.
But the tables were turned after the break as Zak Hardaker, ex-Canberra Raider Jordan Rapana and Lewis Martin all touched down within the space of 12 minutes to give Hull their first home win in nearly a year.
Even though Powell laid the blame for Wakefield's loss on their second-half performance, he suspects Vella could have been affected by what he overheard from Cartwright as the players made their way to the tunnel at the interval.
"We've lost the game, we deserved to lose," said Powell. I'm as disappointed as I've been with this group of players since I've been at Wakefield. It was just not acceptable as a performance.
"We've got to hold our hands up to that but I don't think a referee should ever be influenced. John has not been aggressive to anybody, he's just having some words within ear shot, and it shouldn't work.
"(Vella has) completely flipped his decision-making. We got no penalties in the second half, I'm not sure they got any in the first half. It probably should have been a little bit more even either way.
"Did that have an influence on the game? I think it had an influence. Is it the main one? I just don't think we handled the second half well."
Powell admitted he has been guilty in the past of attempting to sway the thinking of referees but Cartwright vehemently denied the claim after Hull leapfrogged Wakefield into sixth in the table.
Cartwright said: "Did Daryl say that? He's one to talk, isn't he! I didn't influence the referee, I didn't talk to the referee at all. I didn't say a word to the referee."
Asked if he might have said something that could have then been overheard by Vella, Cartwright said: "That's a different story. I didn't talk to the referee.
"We didn't get anything in the first half. We didn't get a penalty or a six to go. I was questioning our players about fighting in the ruck as they were walking up the tunnel."
Hull had lost 11 and drawn one since they last prevailed at the MKM Stadium on July 20 last year, with their previous eight wins in 2025 being on the road to keep their hopes of a top-six finish alive.
A relieved Cartwright added: "You can talk all you like about it not being there but it's there. The fact is we hadn't won a game at home for a long time. I'm really pleased we don't have to talk about that any more."
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