Would a component from Japan that is rated 100 volts be safe to use here on 110-120 volts,
Safe? That's not the problem. The problem is you will be feeding the piece of equipment at a much higher voltage than the equipment was designed to be operated at. Will it work? Yeah,.... But you will shorten its' life.
General rule is + or - 10% of the manufacturer’s recommended voltage.
100Vac x 10% = 110Vac.
The average residential AC mains voltage in the US is 119Vac - 122Vac. 120Vac nominal probably being the most common.
The cheapest way to reduce the voltage to 100 volts is with a Buck auto-transformer.
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