How are switch-mode power supplies better?

The second-generation power supply, called the switch-mode power supply or "switcher" for short, arrived in the late 1960s. By increasing the AC frequency from 50 or 60 cycles-per-second to several thousand cycles-per-second, engineers discovered they could reduce the size and weight of the transformer and significantly improve its efficiency (reduce the amount of energy wasted in the form of heat dissipation).  more