The 20-year-old, on loan from Orlando in Major League Soccer, put the visitors ahead 2-0 with a short-range header in the 49th minute off a headed pass from Mads Andersen after Callum Brittain’s corner kick was only partially cleared.
Dike scored again in the 81st minute with a sliding right-footed volley from 7 yards from Brittain’s cross.
Earlier Wednesday, Dike was selected for the U.S. roster for exhibitions against Jamaica on March 25 and versus Northern Ireland three days later.
Cauley Woodrow had put Barnsley ahead with a penalty kick in first-half stoppage time. Uche Ikpeazu scored for Wycombe in the 85th.
Barnsley has nine wins and three draws in its last 12 league matches and is fifth after 37 games with 64 points, trailing Norwich (82), Watford (72), Swansea (69) and Brentford (67), and ahead of Reading (61) and Bournemouth (59).
The top two teams are promoted to the Premier League at the end of the 46-match league season, and Nos. 3-6 go to a playoff for the final promotion spot.
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