If you mean an unit with a main transformer, then any power supply schematics with voltage and current regulation can be ok.
If instead you mean a PSU without a "main" transformer ..... this involves switching circuitry at 240V potential, and it's not easy, especially if you don't have a possibility to wind-up your own switching transformers ..... the easiest way that come in mind, is to get one of those switching type "wall" adapters, universal (mean, voltage variable), and 2000mA capable, and then modify the inside circuit for get the result you want (but the modifications depends from the type of circuit you find inside it)
Another alternative is to use one of these switching halogen lamp "transformers" in an inusual way (those things are very helpful when you need compact power sources for non standard uses, and usually none think about them
) ..... get one not dipped with resin, ofcourse, open it, unwind the 12V wire (don't touch the thin one) from the output transformer (count the wire turns and divide for 12, for get the voltage that you have as output for each turn), and then rewind it with the turns you need for that voltage, or a bit more (consider that if you rewind it for 6V, half of the original voltage, you can use double size wire and get the double of the power ..... as example, a 100W unit usually give you 8A at 12V, so you can use a wire with the double size and get easily 15A at 6V
), then build a current control circuit as output stage (after a diode bridge and filtering caps, ofcourse).
