idea
The US electrical system is 240 based with split phase. This means that the converter is grounded/neutral in the middle of its secondary winding (the transfer inductor), with 120v potential on each side of it. The electrical panel is typically powered with every other breaker on each of the 120v. By using both of the outputs, they add up to 240v, which is usually used for heavy equipment like washing machine, dryer, stove and furnace.
references
Technology connections / the us electrical system is not 120v is introducing this.