The Devils reached the final by winning their semi-final on Saturday and Brady Kurtz clinched the trophy by beating Workington’s Kenneth Hansen in yesterday’s last heat decider.
Plymouth finished on 30 points with runners-up Workington on 29.
Jack Holder led the way for the Devils in the final with 11 points, dropping only one point in his four rides when he was beaten by home rider Craig Cook in his first outing.
Brady Kurtz and brother Todd Kurtz scored seven points each with skipper Kyle Newman on five.
Host club Peterborough finished third on 25 points with Berwick trailing on 12.
Plymouth dominated their semi-final on Saturday with Brady Kurtz and Holder dropping just one point as they finished five points clear of Sheffield.
Semi-Final Two: Plymouth 23 (Brady Kurtz 8, Jack Holder 8, Kyle Newman 6, Todd Kurtz 1), Sheffield 18, Newcastle 17, Redcar 14.
Final: Plymouth 30 (Jack Holder 11, Brady Kurtz 7, Todd Kurtz 7, Kyle Newman 5), Workington 29, Peterborough 25, Berwick 12.