B-Vent Flue Condensation
To answer your question I suppose it could although I have never seen it.  I doubt your vent cap is too restrictive unless you have or have had in the recent past a bad sooting problem.  I rather suspect the B-vent is not being kept warm enough.  It has to be in a warm space basically all the way to its termination. No drafts.  No cold spots.  Warm.  It should be run straight up or nearly straight up.  And as short as possible and the very least number of bends.  Bends are a killer.  Happy Venting.  P.