Xantrex 6 kw series
XDC 6000 Watt and 12000 Watt Series
Digital Programmable DC Power Supply
1st digit is voltage, second digits are amps
XDC 10-1200 = 10 vdc at 1200 amps
XDC 20-600
XDC 30-400
XDC 40-300
XDC 60-200
XDC 10-600
XDC 20-300
but you have other series on different makers ... theses are the most efficient and small as you can get, they are smps based / phase controlled etc ... not linear
forget about building a simple psu ... unless you try to gobble a car battery charger into a power supply, some of them had variable core on the xformer, but they are very crude supply with low stability, the car battery act as the capacitor, and they are not meant to run continuously, they heat a lot and will bust
and normally they are 12-14vdc devices and for sure you can't adjust the voltage down to nothing