Are you sure Volts is the term you mean to be referring to?
US Standard AC Voltage is 120V (+/- 10%) for small/regular appliances and 240V (+/- 10%) for large appliances (I.E laundry dryer big 3 prong plug)
US Standard DC Voltage is 12V
Any product you buy should run at 120V if it's AC and 12V if its DC. If not it should have an inverter box between the wall plug and actual device that will adjust the V to the products requirements.
I'm guessing the question you are trying to ask is:
"What driver do i need to power 30 CREE XP-G at 1200 mA?"
Check out Reefledlights.com they are local, have lots of DIY info on their website and you can check out their driver selection to figure out what suits your individual needs.
- Please correct me if im wrong in my assumption, just trying to help