Power supplies are rated for 100V because that's the voltage in Japan. Though the tolerance would probably be useful for running a really long US extension cord.
My old computer started burning in some internal cabling about 30 years ago. Turns out our power wasn't 230 V when the power company came and set up a machine to make a graph. Some times of the day it could be much lower and that made my ancient atari converted to a towerbox to burn the cable to the harddrive on booting.