Power Supply external voltage 115v or 230v?
 

Exactly as title says.

Currently running a BFG GS-450w I just installed.

What do I set the external voltage to?

Depends what you're plugging it into, but with normal wall power anywhere in North America, it's 115.

Going into a surge protector "transformer" socket, into a wall outlet.

"Depends what you're plugging it into," was slightly facetious... I mean if you were plugging it into something like a heater or stove or dryer plug, you'd need to set it to 230V, but you'd also have to build a custom cord for that.

The cord that comes with North American power supplies, will only plug into a 115/120VAC, 15A outlet, meaning the ONLY thing you should be able to plug it into is a 115/120V outlet.

For 99.99999% of the people in North America the setting will be 115V.