High-flying Port Vale stretched their unbeaten League Two run to four games as they came back to win at Home Park.
Argyle left-back Robbie Williams rocked Vale with a 30-yard left-foot strike.
But, having trailed 1-0 at the break, Ashley Vincent earned a 66th-minute penalty, coolly converted by striker Jennison Myrie-Williams.
Vale won it with two late goals, winger Vincent firing in from Myrie-Williams' slick pass before Ben Williamson converted Doug Loft's cross.
Home skipper Darren Purse thought he had pulled a goal back but his header was cleared off the line by Loft.
Vale's run of 10 points from a possible 12 lifts them up to second in League Two - three behind leaders Gillingham, Adams' old club, who they host next Saturday.
VIEW FROM THE DRESSING ROOM
Plymouth Argyle manager Carl Fletcher told BBC Radio Devon:
"We're a little bit shell-shocked. We've come out of that thinking 'how did we lose that one'?
"We controlled the game in the first half, played some really nice stuff, got a deserved lead, tried to push on second half and almost got sucker-punched a little bit.
"It was just disappointing to lose the goals in the second half. We spoke to the players about doing the right thing whether you're winning or losing.
"If it's the right thing to do in the first half when you're winning, getting joy from it, it's still the right thing to do in the second half.
"It's hard to put your finger on [what went wrong]. Losing goals makes a difference obviously."