You are right, power supply improvements are asymptotic. It's not just about total efficiency, but also about how the heat is generated and where you can put it

You are right, power supply improvements are asymptotic. It's not just about total efficiency, but also about how the heat is generated and where you can put it. A lot of the newer developments don't do a lot for total efficiency but produce smaller supplies by more efficiency managing heating. That said, most supplies for sale are based on old, fossilized designs created ~10 years ago, hovering at around 80%. If you spend more you can get the gold, titanium, etc. But then, even those tend to be below the maximum you can get, which is closer to 98% if you have information about your load. You can also design the system to have better efficiency at various loads. Typically half, but could be worth tracking newer CPU/mobo/GPU developments.