Circuit on the right is a conventional full wave split rail supply. The resistor has been adjusted to match the current load on the synchronous rectifier on the left, this circuit uses P channel but could just as well be N channel mosfets to replace the the diodes in a conventional supply. Notice how much more efficient it is. The 2 diodes in parallel with the mosfets only represent the parasitic body diodes found in mosfets and can be deleted for the purposes of the simulation but would be their in the real circuit and only conduct for about a millisecond until the moss fires up and shorts them out.
This is a somewhat idealalised circuit but demonstrates the principal of modern high efficiency power supplies achieving over 90%
