Could drinking vinegar make my kratom capsules work faster?

Theory-- No: Biochemical Fact--increasing the acidic level raises the amount of active ingredient dissociating, not the speed. More of the active ingredient may be available to be absorbed, but the reaction will not happen any faster, and effectiveness and outcome are not guaranteed for the substance you are talking about. Likewise, decreasing the acid makes less dissociate, to absorb less. So No.