What is this red switch on the back of my power supply?

I think it has something to do with voltage, it's set to 115 right now. I have a cooler master extreme, power plus 500w power supply. I'm learning a lot about computers and I need to know what that is, google is giving me COMPLETELY varied answers so I'd rather hear it from a single person or a few who... show more I think it has something to do with voltage, it's set to 115 right now. I have a cooler master extreme, power plus 500w power supply. I'm learning a lot about computers and I need to know what that is, google is giving me COMPLETELY varied answers so I'd rather hear it from a single person or a few who know what they're talking about. Thanks, will choose a best answer.
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