"Two-generation PC power supply" means long life power supply to be available as it is even when generation of PC has changed.
Generally, PCs make rapid progress, and are going to have generation change in one year to two, or even in half a year. However, our power supply can be continuously used unless it changes its basic specification even after CPU or other components have been upgraded in PCs.
We named this power supply hoping the it may lasts from generation to generation, like from parents to children.