12vac Landscape Lighting Transformer - 12vdc?
Are they incandescent bulbs? (IE: Not LED).   Incandescent bulbs don't care about A/C or D/C. So yes, you can power the bulbs with a DC power supply.
Regarding A/C being better than D/C for range:  again, doesn't matter.  Wire size, distance and power draw determine voltage drop.   A/C and D/C voltage drop would be about the same, all else being equal.