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I live in the US, and I am traveling to Japan for a few days.

I want to know if I need an adapter for my USB Wall Bricks.

  • None of them are three pronged, all of them have just two prongs.
  • I do not have any "appliances", like a lawn mower or a toaster. I am just talking about some things I can carry with me so that I can charge my cell-phone, laptop, watch, etc.

I checked this reddit FAQ and this Power Plugs website, but I am getting some confusing information.

I would imagine that the frequency/voltage difference shouldn't matter as long as the prong fits in. I guess the USB bricks would have some stabilization mechanism built in. Right?

Edit: I am in Japan now, and my gadgets haven't blown up or caught fire even though I am still using my power bricks from the US

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  • For complete peace of mind, buy a quality USB charger locally when you arrive. Or ask the place you're staying for one.
    – Criggie
    Apr 28, 2023 at 2:21
  • @Criggie that's poor advice financially, as "quality USB adaptors" in Japan are literally the same stock as in the USA.
    – Fattie
    Apr 28, 2023 at 11:44

5 Answers 5

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I want to know if in Japan I need an adapter for my USB Wall Bricks.

The answer is

No.

(One interesting point - no such 'adaptor' exists! Because there is nothing to adapt.)

The whole issue can be instantly resolved by, obviously, glancing at the specs printed on power plugs, where one will instantly see they (of course) operate perfectly in all of Japan.

Just as the OP mentions, it's one of those curiosities where the interweb is filled with misinfo.

I'm adding here the two most important comments on this page, which say it all:

"That answer is very misleading. Can you point to ANY device that works in the US but not in Japan ? I've worked in electronic product development for 30+ years and I have never encountered something that wasn't compatible"

Key point highlighted.

"You absolutely do not need any adapters. I go back and fore between the two countries (with literally cases of equipment) all the time. Any other information you hear, is wrong."

OBSCURE CAVEAT !

It occurred to me that. Let's say you are, perhaps, an audio or video engineer and or indeed a person who manufactures electrical equipment or such. It's possible that part of your life is using things like this ...

enter image description here

of course, obviously, such things that literally manipulate the electrical supply and are used by electrical supply engineers are irrelevant to this discussion, and some models only work with one very specific power source, or whatever.

Of course obviously you can't casually use such stuff unless you know what you're doing, and it's inconceivable any power engineer, etc, would be asking the question on this page.

(Note that, as a curiosity, the thing in the photo if you ! merely plug two of them in series ! you've just done an incredibly dangerous thing; the issue is completely outside the question "Are Japan/US power blocks interchangeable, answer Yes".)

Excuse my incredibly ugly carpet BTW.

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  • 1
    The comment (actually answer) you added on the question mentioned that you actually have experience doing this frequently. I think adding that information to the answer would improve it quite a lot.
    – T.E.D.
    Apr 26, 2023 at 14:02
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    Perhaps, but for my money "I've done this exact thing and it works" answers are on a whole other level than "in theory this should work" answers. Nothing wrong with leaving the rest with something like "If you think about it, this makes perfect sense ..." Data > Theory
    – T.E.D.
    Apr 26, 2023 at 14:48
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    @Fattie I am leaning towards the answer being factually wrong on that point. 100V/120V transformers do exist and there are plenty of choices on Amazon. There are problems people have had with audio gear imported from Japan when naively assuming that they can be run without one. There are warnings that components with high voltage components like Electrostatic Drivers can be dangerously overvolted without using a transformer, however I do not know how true that is. I am also unfamiliar with any issues going the other way -- 120V60Hz->100V50Hz.
    – Chuu
    Apr 26, 2023 at 16:47
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    If you're looking for any device, I've got an Atari 2600 with a 60Hz/115V linear-regulator power supply. I've got zero interest in actually plugging it into a Japanese 50Hz/100V outlet to find out what happens.
    – Mark
    Apr 26, 2023 at 20:51
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    @Tiercelet I often travel with a few (US) power strips because it's inconvenient buying them whilst on a project. I may misunderstand your question but all US/Japan power strips work in both Japan/US. Also pls note, almost all extension cords and 'power strips' are, in fact, incredibly badly made and dangerous and badly specified. (This is the exact reason, that housing codes now specify vast numbers of power outlets in the walls, closely spaced, to fight against extension cables/strips.) So conceivably an answer to your question is "only use incredibly "over" rated ones anyway!" IDK.
    – Fattie
    Apr 27, 2023 at 14:13
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Japan's power grid is a bit special, in that the eastern/western sides are 50Hz/60Hz respectively.

If we're not talking about USB power bricks, then the frequency may matter (especially for motors) because that 50/60 difference is about 15-20%, far more than typical tolerances of motors. Japan's voltage of 100 is also quite a bit below the expected 120v for US devices.

However, USB power bricks are not motors. In fact, they are typically rated for 100v-240v by default because they are something called Switched-mode power supplies. These power supplies are universally chosen for USB bricks due to their small size. It also means that they are usually made to support 100v-240v @ 50Hz-60Hz by default because there is no advantage of limiting it otherwise (check the device label).

There's zero chance that your USB brick is anything but this, because other transformer types are bulky and large.

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    The undervolting Q you link to is about low-voltage DC circuits. USB bricks contain switched-mode power supplies that convert high-voltage AC to the 5V DC required for USB, ensuring the output is within spec in the process. Apr 26, 2023 at 6:18
  • 1
    I'm not sure what happens If you have a transformer rated for 120v, but you feed it only 100v. Technically this condition is called a brownout, and extended brownouts can damage motors, but I can't find reliable information about other AC devices.
    – Nelson
    Apr 26, 2023 at 6:23
  • 13
    Yes, that can happen if you have a linear transformer, but as noted small electronic devices like USB bricks use switched-mode power supplies that can accept a wide range of inputs (hence the ubiquitous 100-240V label) and do not have this issue. Apr 26, 2023 at 9:28
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    Lamb has flawlessly explained the situation. Whilst well-meaning, this answer (which will now live on the internet forever) is exactly the sort of misinformation the OP mentions in the question.
    – Fattie
    Apr 26, 2023 at 11:40
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I would imagine that the frequency/voltage difference shouldn't matter as long as the prong fits in.

You would imagine wrong. That's how fires start.

You'll need to check the expected voltage for the USB bricks, it should be written on them. Most mobile adapters are supposed to work with the full range of voltages/frequencies, so you'd see something like 100-240V ~ 50/60Hz (See an example here). However it may be that for some reason your specific brick is only rated for a sub-set of the worldwide power specs, and you should check that before plugging it in.

The prongs themselves in Japan are the same as in the US.

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  • Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Travel Meta, or in Travel Chat. Comments continuing discussion may be removed.
    – JonathanReez
    Apr 27, 2023 at 17:09
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I checked this reddit FAQ and this Power Plugs website, but I am getting some confusing information.

No surprise. Japan is one of the more confusing countries out there when it comes to the power grid and power plugs. Half the country is on 50 Hz, half is on 60 Hz, and all of it is on a lower voltage than most of the world (100 V), but the JIS C 8303 plugs are almost (but not exactly) equivalent to NEMA 1-15 and 5-15 plugs.

I would imagine that the frequency/voltage difference shouldn't matter as long as the prong fits in. I guess the USB bricks would have some stabilization mechanism built in. Right?

The good ones should handle this fine. The problem is that you may not have good ones. I still occasionally see cheap USB power adapters that do not properly support anything except the local line frequency and voltage.

In general most devices with NEMA 1-15 or 5-15 plugs will mechanically work with Japanese JIS C 8303 sockets. You may have issues with devices with polarized plugs in older buildings, as older JIS C 8303 sockets were unpolarized.

Electrically, many, but not all, solid-state power adapters for modern electronics sold in the US will work just fine in Japan. You should check each individual device, it should have information somewhere (often for USB power bricks it’s on the side that faces up against the outlet when plugged in) that says something like 100V-240V @ 50-60 Hz. The important part here is that the lower voltage is 100V or less, and that the frequency covers both 50 Hz and 60 Hz. If the device does not meet those requirements, or does not list this information, do not use it without an active adapter (best case it simply won’t work, worst case it will fail destructively and possibly dangerously).

Older power adapters that include an AC transformer or devices that run entirely on AC power are very likely to not work at all, and are also pretty likely to fail in very dangerous ways (think catching fire or exploding). It’s unlikely you will have anything that fits this unless you’re dealing with devices from before 2000.

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  • Just to continually beat a dead horse. The reason this answer is, in essence, Wrong, is that the phrases are very poorly chosen. Hence: "Good ones .." -> "Virtually Every One". "Occasionally see .." -> "Unheard of in reality." "In general .." -> "Does." "Many but not all" -> "All". "You should check .." -> "If you want, go ahead and check and you'll see it's true". And so on. It's just very confusing. The answer to the OPs question is nothing more than "yes"
    – Fattie
    Apr 27, 2023 at 14:17
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    @Fattie I have practical experience within the past few years that contradicts the assumption that all modern solid state electronics fully support all internationally used voltages and standard line frequencies. It’s not common any more to find consumer devices that lack such support, but such devices do still exist, and given that getting this wrong is a potential safety hazard and not just a financial issue, I’m strongly of the opinion that people should be checking their devices instead of blindly assuming things will work. Apr 27, 2023 at 19:00
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    @Fattie When the stakes are high (fire) and the effort is low (read the label), why would you not check?
    – Mr47
    Apr 28, 2023 at 7:31
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    @Fattie Last month an USA colleague visiting Germany plugged in his laptop with an "universal" travel power-adapter (solid state) that he bought specifically for his trip. Boom!. Minor explosion. Luckily nobody was close to it. After the smoke cleared and we reset the circuit-breaker we took a good look at the remains. Even though it was sold as "universal" and "world-wide use" and came with a selection of detachable international power-plugs, it was only rated for 110V-125V/60Hz. (240V/50Hz here.) The laptop got fried too. (Good thing he had backups. SSD was fried and not readable anymore.)
    – Tonny
    Apr 28, 2023 at 11:13
  • @Fattie Continued.. Manufacturing date on the power-supply was 2022. Not old stock from way back. At least this particular one is not longer sold by Amazon. They removed the vendor completely. Apparently we were not the only ones with complaints about their products.
    – Tonny
    Apr 28, 2023 at 11:16
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My USB power bricks work fine here in Japan. Absolutely seamlessly for my cellphone, laptop, tablet and smartwatch. Nothing caught on fire.

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