revision preference src: Electric trains were due to start on 1 December 1925. Power supply problems meant that the introduction of electric trains from Charing Cross and Cannon Street to Orpington was postponed until 28 February 1926. <SEP> tgt: Electric trains were due to start on 1 December 1925, but power supply problems meant that the introduction of electric trains from Charing Cross and Cannon Street to Orpington was postponed until 28 February 1926.