It is a mess. Nowadays all devices support both frequencies, but I have heard from Japanese colleagues that back in the day if you moved accross the frequency b

It is a mess. Nowadays all devices support both frequencies, but I have heard from Japanese colleagues that back in the day if you moved accross the frequency boundary, you needed to replace your appliances. Maybe that's one of the reasons why Japan has a huge second hard market? But the real problem came after the Tohoku earthquake of 2011, when several powerplants in the Eastern half of the country went offline, and they couldn't not transfer enough power from the Western half. There are a few conversion stations, but their capacity was not enough, and as such the Eastern half endured long black-outs even though the country had enough surplus power generation capacity.