There has been a lot of speculation regarding the next-gen PCIe 5.0 12-pin power connectors due to a wide variety of reports regarding how much power they will be able to output. The typical speculated output value is generally around 600W.
It looks like Asus has finally answered this question as its recently released ROG Thor series of power supplies has been rated to be able to deliver up to 450W of power via a 12-pin connector. The information comes from the Asus ROG Thor 1000W Platinum II PUS's "PCIe Gen 5.0 Ready section".
However, the firm had apparently altered this key piece of detail very recently as VideoCardz says it had noted Asus previously stating on the page that the 12-pin PCIe 5.0 power connector "can pipe up to 600W of power to PCIe Gen 5.0 graphics card". Hence, it looks like Asus too was probably overestimating the amount of power such a 12-pin connector could actually provide.
While a 25% reduction from 600W down to 450W is significant, we must remember that going from (6+2) pins or 8-pin power connectors up to a 12-pin model is still a massive upgrade as the 8-pins can only provide 150W while 12-pin cable is set to deliver thrice as much power.
PCIe 5.0 will also bring 600W of output but with the 16-pin (12+4) pin connectors instead. This is also why there is conflicting information regarding the power headroom of the purported EVGA RTX 3090 Ti Kingpin model as it reportedly comes with either dual 12-pin connectors or dual 16-pin connectors.
If the Kingpin packs dual 12-pin, then the card will have a 975W of power headroom, while for the dual 16-pin model, expect 1275W of power headroom.