You might be surprised: my Amiga 4000T with a 68060 processor, and full complement of cards (graphics, network, sound) has no fans other than the case fan - all running off a very modest (by current standards) power supply: because there's very little heat generated.
And while I'm missing many of my favorite modern apps, for many tasks the productivity is still unequalled: near-instant bootup, hugely responsive, and a beautiful elegant operating system.
It was more about the parent's post SGI nostalgia.
It's all nice, but my machine's power adapter is 60W. That's its maximal theoretical output. (okay, with 90% efficiency that's 67W). It typically uses 20W to 40W depending on the load.
Plus, it auto-sleeps. Then it consumes just about 1W. Talk about efficiency.
And while I'm missing many of my favorite modern apps, for many tasks the productivity is still unequalled: near-instant bootup, hugely responsive, and a beautiful elegant operating system.