The Dell Pro Max PSU + enclosure is only rated for 240w, it literally can't pull more than 250w from the wall without shorting itself.
280w according to the spec sheet I just looked at.
Also just look at the graphs on Geerling's website. The Mac Studio eats the Dell for breakfast in a number of the tests: https://www.jeffgeerling.com/blog/2025/dells-version-dgx-spa...