SETI also runs (or did, from what I remember) a 3D screensaver. It's not doing nothing on the videocard, anyway, but I don't know how close to fully maxing out anything it gets.
Talking about power load, though, I have a Kill-A-Watt pass-through power meter, and I have measured power at the wall exceeding the rated output power capacity of an 80% efficient power supply on a computer running at full load (running a graphically and computationally expensive computer game).
A lot of PSUs are pretty inefficient. You can look up the stats. It wasn't until recently that you even had a lot of them earning the 80 Plus "bronze" rating, which is 80% efficiency. There's still plenty with worse efficiency than that. A decade ago, you're probably looking at 60% efficiency on average.
Talking about power load, though, I have a Kill-A-Watt pass-through power meter, and I have measured power at the wall exceeding the rated output power capacity of an 80% efficient power supply on a computer running at full load (running a graphically and computationally expensive computer game).
A lot of PSUs are pretty inefficient. You can look up the stats. It wasn't until recently that you even had a lot of them earning the 80 Plus "bronze" rating, which is 80% efficiency. There's still plenty with worse efficiency than that. A decade ago, you're probably looking at 60% efficiency on average.