Yamaha used to have national service training. One year, the B6 and "X power" were both introduced. B6 looks like Darth Vader. It has a Carver magnetic field power supply, and is rated at 250w/ch. Yamaha set it up on loads and plugged the power into a 30 amp variac. They had the amp running full power into 8 ohms, then began to lower the AC voltage on the variac. pretty soon the amp was grunting, and every light in the room was madly flickering as the switchmode was making up for low voltage by drawing more current. The demo was impressive! IIRC the AC voltage was reduced to 85 volts.