Straight from Apple's HW developers site:<BR><BR>Processor and Bus Slewing<BR>To lower power consumption and heat generation, the iBook G4 incorporates an automatic power management technique called ...
An old iBook G3 Clamshell from 1999 was modded to support USB-C PD for power. The modder replaced a blown SMD zener diode with a through-hole one and used a USB-C PD trigger board to power the laptop.