A thing to take note of when choosing a PSU is that their output diminishes over time...due to capacitor aging. While you may barely squeak by within the limit at some point your output will fall below the minimum.
I respectfully disagree. A 1000W + PSU seems a bit overkill. Sure it's nice to have headroom for future expansion but unless he plans on running liquid cooling and a 2-way SLI 1000W is not really worth the extra cost.
I've found that 850W is a pretty solid option unless you want to stack multiple graphics cards. 850W gives you all the power you need and some head room for future expansion. Newer graphics cards are way more power efficient so I don't think it too outrageous to claim that an 850W GPU is capable of a SLI setup if that's something that interests you.
I'd say a 750W would be a good start for you in a singe GPU set-up.
See that depends.
Number of drives both mechanical and ssd. There power requirements.
What if he decides to throw a few ssd I'm the future in raid 0 configuration for fastest boot and read times.
Also depends on the number of optical drives.
And what else may be installed in the pc.
Lastly buying a good 1100watt one know means not worrying about the power supply for many years. Requardless of upgrades placed in the system.
Also let jot forget fans require power as well. There two ways to do this.
Find out the power rating of the every item in the pc and it load requirement then add that up and makes sure to have extra capacity to add additional items. But make sure to add to your calculation before buying them.
Or go twice your max load and know unless your going to ski you video card you be hard pressed to every go over the limit for that pc.
That the model I hem using for 20 some years and the only time I look a new power supply is if the new video card I am buying needs more power. The I get a new powersupplly and move that one to pc that getting the older video card
