If i change the voltage on the back of the power supply,how will it affect my PC?

I have a iPhone that im trying to connect to my PC. However, I don't have enough %26quot;power%26quot; because it is connected to a USB Hub. The hub is bus powered, because i don't have the AC adapter for it. If changing the voltage helps, please tell me, and if not then tell me the affect, because im curious anyway.If i change the voltage on the back of the power supply,how will it affect my PC?
If you change the voltage on the back of your computer, you'll fry the power supply and possibly the rest of the computer.

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