Unfortunately for the 14900k, system load isn't 400 W. It can be as high as 609 W even after enforcing a 125 W power limit. At default settings, Techspot measured another 100 W over that for over 700 W system power draw.
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They claimed a total system power of 527W for the 14900K. The ~400 was supposedly for the 285K.
It will also vary obviously a lot depending in the testing setup and what was tested so it's roughly consistent with Techspot stuff. They might have manipulated the game list somewhat so that the 14900K looks less the power consumption monster it is.
We will know for certain when reviewers actually test this claim.
But if it's consistent with Techspot test then it would be 7800X3D at 477W vs 285K at ~529W.