[Silicon]

Some of these Farnell power supplies have several secondary windings.
There is often a third winding to power the PCB circuit.

The connections can be varied to reduce or increase the amount of secondary voltage going to the rectifier.

If the power supply is running at a fixed voltage, the windings can be optimised to reduce the heat dissipated in the pass transistors.

The previous user may have also modified the winding connections.