Right now is a transition period. The standard ATX 2.0 we all know and love has a new design and specs, the ATX 3.0, which currently has no requirements as Darkbreeze said. Which beggars the question, 'what about tomorrow?'.
It's entirely possible that within 1-2 generations of gpus, or possibly even cpus/motherboards, you'll start seeing equipment (especially the uber high end or expensive giant wattage hogs) that will specify a requirement for a ATX 3.0 psu.
So as Darkbreeze so nicely put it,
Aside from that, all current hardware works perfectly fine with existing standard power supplies.
The question then becomes 'do you really want to spend $200 on an excellent, high quality, power efficient watt monster with a 10-12 year warranty, that you'll need to replace, most likely, long before that warranty is up.
Need? No, no need currently. But it honestly wouldn't hurt if planning on keeping that monster for the next 10 years and upgrading to a cpu/psu that may require one, later.
If I was building from scratch, and opting for a 40series nvidia, I'd probably also opt for the ATX 3.0 psu as well, it having native 12vHPWR connectors, just so I wouldn't have to deal with the 4x8pin to 12+4pin adapters and cable management. And that's besides the advancement in specs and abilities the 3.0 has over the 20year old 2.0 specs.
https://www.tomshardware.com/news/intel-atx-v3-psu-standard