A typical circuit in a US home is 120V, 15A. That is about 1800W which works out to about 1600W out of a supply like this at 80PLUS Gold efficiency. You'd trip a breaker if you tried to pull 2000W from a single wall outlet, and that is where the limitation comes from. 240V is widely available in the US, but in residences it's typically only found in certain locations for your range/oven, AC, dryer, etc. If the designers were generous with trace cross section and input components such that the increased current isn't a problem, you could use this supply at its maximum capability with 120V if you're on a 20A circuit. 120V, 20A circuits typically use a T-slot outlet. You'd be able to quickly identify it if your room had one.