AT power supply handled +5 and +12 volts, +5 for ISA and processors, +12 for motors in disk drives. In 1995 486DX2 was introduced with 3.3V core, so it derived that from a simple but inefficient linear regulator connected to the +5V rail. In 1999 Athlon was introduced, which consumed 60W of power through +5V line, with total current up to 30A. Power supply cords started to burn under high loads. In 2000 Pentium4 was introduced, which had processor core voltage derived from +12V line, not from +5V.
I'm asking, what could be better if linear regulators to power 3.3V processor cores in 1995 where fed from +12V line, not from +5V?