No-Load losses on the power conversion seems to be the real issue and is rarely mentioned and understood even less often. Plus the conversion eff. curve.
Eg: I shaved ~40W off the idle load on a server (250->210W) by doung nothing more than removing the redundant supply
You just reminded me of a funny story about redundant power supply.
A college buddy used to work at Motorola (I'm naming the company because they wouldn't mind this story being shared) back in the late 90's or early 2000's. They had redundant power to their campus, bought from two different companies, coming in on opposite sides of the campus, so that even if some backhoe operator cut a ground-based power line somewhere, they wouldn't lose power.
And yet, one morning, the power went off all across their campus. After a little investigation, they sent pretty much all their employees home at noon and told them "take the afternoon off, don't come back until tomorrow, you wouldn't be able to do any work anyway". Turns out that although the power lines came in at opposite sides of their campus, somewhere a few miles away both of the power lines feeding their campus ended up running through the same underground conduit. And yes, a backhoe had managed to cut that conduit and break both of the lines they depended on at the same time. They had a single, VERY non-obvious, point of failure, and the backhoe had unerringly homed in on that SPoF.