Yea I think if you run the calculations and you have room you should be good if your PSU is just slightly above the power requirements. If you run an unusual amount of memory or HDDs/etc, you might want to calculate everything manually rather than just assume its 100 watts though.

I have never had a PSU fail, but supposedly unlike pretty much every other component if it fails its possible it will destroy your GPU/CPU/MB so it makes sense to spend a little extra on a good PSU.

Probably my best component purchase ever was a 1050W Modular PSU in 2014. It was an old model even then and apparently no one wanted 1000W+ power supplies back then because it was on clearance. It should still be good for a 3090 and probably even a 5090 when I upgrade again in the future.

I paid far less than a 1000w PSU costs now.

> Nvidia recommends a much more powerful PSU than needed just in case.

The two things to watch out for here are

1) Cheaper PSUs can't always actually hit their claimed wattage, particularly not in real-world heat scenarios

2) CPU & GPU both use the 12V rail for their power, and not all PSUs can deliver all the rated wattage on the 12V rail.

Any decent to good PSU won't have either of those issues, most list their rated wattage entirely on the 12V rails these days.

So for example let's assume 250w for the GPU average and 120w for the CPU average (turbo & boost & all that). A 400w PSU could technically do that, particularly since if your only drive is an SSD your "accessories" are basically a rounding error. But if we take this 400W PSU for example: https://www.newegg.com/coolmax-i-400-400w/p/N82E16817159140 it can only deliver 300W on the 12V rail. Not enough. By comparison this EVGA 450W PSU can do a full 450W on the 12V rail alone: https://www.evga.com/products/product.aspx?pn=100-BR-0450-K1

That's a 150W useful difference in this scenario even though the "rated" power only differs by 50W.

I feel like this used to be more true in the past. These days CPUs can exceed their official TDP by quite a large margin, and while in theory they should only do so temporarily, many motherboards default to unlimited boost clocks. (Then again, perhaps you're never going to fully utilize both CPU and GPU at the same time...)

You can see on Nvidias product page they are calculating based on a 125W processor. My 3700X is 65W so I'll have enough room for a 3070 easily on a 600W PSU.

Do note that a PSU running at max capacity might also cause a noisy hot PSU.

Having some headroom might result in a quieter system

My old theory was they add so much headroom that you might be able to add a second one later in SLI.