The provisions as set forth in § 3 hereof are intended to supplement or to supply authority in the county commissioners of the various counties to do and perform various acts, matters and things not otherwise provided for by law. In any county where there shall already exist authority under any public local law to do or perform any matter, act or thing referred to in § 3, said public local law shall prevail and completely control the acts and procedure of said county commissioners unless said public local law is more restrictive than the authority granted under § 3, in which event § 3 shall be deemed to supplement and increase said authority. Nothing contained in § 3 shall in any manner be considered a limitation or restriction on any existing power and authority granted the county commissioners of any county nor shall any broader or more unrestricted power or procedure vested in or authorized to the county commissioners of any county with respect to any matters specifically provided for by a public local law be deemed in any manner limited by any of the provisions of § 3.