Some EVGA models are made by Seasonic.
Some are made by SuperFlower (the G2 and P2 series in particular, VERY well done).
Some are made by .... dunno.
Corsair makes NONE of it's own power supplies, they contract them all out - and depending on who makes each model, they can be very good to very poor.
Seasonic on the other hand DOES make all of it's own - and they are generally Very Good to Excellent (though I hate their "crap fan" choice on the Prime series and won't touch those).
It's interesting to trace down who makes each brand - when you get down to it, I'm pretty sure there are only about 15 perhaps 20 actual "ATX power supply manufacturers" in the world, and almost all of their factories are in China or Taiwan.
It's NOT quite as "centralised" as Hard Drive factories in Thailand though....