Pico DC DC modules.
Going all 12V concept is very very good and higher efficiency, helps with cost somewhat, and forces motherboard makers to be more efficient using switching regulators as well. HP was doing this much earlier starting with zx00 and elite 8000. Even HP used 11V standby power instead of 5V.
The most of PSUs for last 8 years have gone to main 12V power supply only, and used sub DC-DC converters fed by single 12V PSU output to generate 5v and 3.3V. So this is easy step for PSU makers to go all 12V.
I was waiting for that to happen for newer computers in future when I happens to buy one.
Lower voltages 3.3V and 5V usually goes higher losses you get trying to generate voltages with one transformer (typical!) due to space limitations in a PSU chassis and cost, in older PSUs also harder to design regulating individually voltages so these had to go by group regulation monitoring one of voltage as fixed value while other voltages fructrates somewhat.
Notebooks have been doing this already. Either from power supply adapter of one voltage output or using battery's one voltage to feed DC-DC converters on the notebook's motherboard. Not in series of DC DC converters. There is no charging circuit on the notebook motherboard's. The battery pack has communication for status and charging circuit built in.
Cheers,
Great Northern aka Canada.