The "three wires vs. four wires" situation could possibly come from the
fact that your transformer has two separate 18V secondary windings while
the other transformer probably has a center-tapped winding. There is no
difference in functionality as long as one connects the proper ends (in the
four wire scenario).
fact that your transformer has two separate 18V secondary windings while
the other transformer probably has a center-tapped winding. There is no
difference in functionality as long as one connects the proper ends (in the
four wire scenario).