Someone gave me this generator, with no manual. And I have a question about it. I'm to lazy to explore the internet for an answer, other than looking for an owner's manual, which what I could find wasn't much help. See attached photo. See the L14-20 plug? It's labeled 120/240V, and 20 amps. My question ... What determines whether the electricity coming out of that plug is 120 or 240V? It can't be both. Is it the user configuration of the plug that goes in which makes the determining factor? Thanks.