I can only surmise that the potential confusion comes from the two apparently conflicting certification marks.
The first is for Japan, [PSE] & 2nd the US [CULUS]. I didn't dig into the depths of each certification method, but it's reasonable to assume the Japanese one is intended for international & the US only for domestic, to tick the 'safety' boxes for each territory.
The manual says basically 'use a plug adaptor for abroad', no voltage transformer needed. Any 'tourist/travel adapter' plug converter will be fine. There's no Earth on devices such as these, as they're classed as 'double insulated' so it will go in any socket, any way up.
From the manual - page 31
The battery charger can also be used in foreign countries.
The battery charger is compatible with a 100 V AC to 240 V AC 50/ 60 Hz
power source. If necessary, attach a commercially-available plug
adapter for the respective country or region. Do not attach any
portable voltage transformer to the battery charger. Doing so can
damage the battery charger.