Not sure if that is the high voltage most use or not. Most HPS lights are 277v ac well above 400w anyway. I think the 175w & 250w bulbs are also 277v but I have not used that small of a wattage in years.
Zandor Reviewed by Zandor on . UPS vs. Ballast question As I have quite the background in computer technical work, I wonder if I may use my APC UPS Backup Pro 280 in lieau of a ballast for now for a few seedlings I have? The UPS is rated for 480 joules, (Output- Output power capacity 280 VA Output power capacity 180 watts Max Configurable Power 280 VA Max Configurable Power 180 watts Nominal output voltage 120V and input- Nominal input voltage 120V Input frequency 50/60 Hz +/- 3 Hz (auto sensing) Input Connection Type Rating: 5