I honestly do not know of anything other than having the systems power one large switching powersupply. Sorta a merge? In series though you just need to replace the ground with the other 12v from the othe rPSU and keep them electrically separate. Still a lot harder than buying a psu to provide. But those little PSU's do look nice.
The meanwell 600-24 provides 600watts at 24volts
(thus the name)
As for getting better temps, by lowering the voltage the efficiency is increased, and as long as the movement wattage is still enough to move your heatload it will work quite a bit better at load. Thus with a huge TEC you can tune more