Just How Dodgy Are Cheap USB Chargers Anyway?

Aside from apparently having both the ability to reproduce on their own and simultaneously never being around when you need one, USB chargers seem innocuous enough. The specs are simple: convert mains voltage to 5 volts, and don’t kill anyone while doing it. Both specs are typically met by most designs, but judging by [DiodeGoneWild]’s latest USB charger teardown, the latter only just barely, and with a whole lot of luck.

The sad state of plug-in USB power supplies is one of [DiodeGoneWild]’s pet gripes, and deservedly so. Most USB chargers cram a lot of electronics into a mighty small volume, and are built to a price point, meaning that something has to give in the design. In the case of the two units he tears apart in the video below, it’s pretty clear where the compromises are. Neither unit met the specs on the label in terms of current supplied and voltage regulation, even the apparently more capable quick charger, which is the first to go under the knife. The PCB within holds some alarming surprises, like the minimal physical isolation between the mains part of the circuit and the low-voltage section, but the real treat is the Schottky diode that gets up to 170°C under full load. Safety tip: when you smell plastic burning, throw the thing out.

The second charger didn’t fare any better; although it didn’t overheat, that’s mainly because it shut itself off before it could deliver a fraction of its rated 1 amp output. The PCB construction was shoddy in the extreme, with a squiggly trace standing in for a proper fuse and a fraction of a millimeter separation between primary and secondary traces. The flyback transformer was a treat, too; who doesn’t want to rely on a whisper-thin layer of cheap lacquer to keep mains voltage out of your phone?

All in all, these designs are horrible, and we have to thank [DiodeGoneWild] for the nightmares we’ll have whenever we plug into one of these things from now on. On the other hand, this was a great introduction to switch-mode power supply designs, and what not to do with our own builds.

48 thoughts on “Just How Dodgy Are Cheap USB Chargers Anyway?

    1. But this item has 500 5-star reviews on Amazon! Surely you trust the internet!

      I agree though – I’d like to know what’s not trash, because there are plenty of more expensive chargers that also manage to fail to shock the proverbial monkey.

      1. Many years ago I did most of my shopping on Amazon. The review system was pretty good. It was the major selling point for me.

        But now everything is ShangDongPing, 5 star rated garbage. Amazon is my last resort now.

      1. Can confirm. They’re well built and follow all safety regulations. I only purchase chargers and LED lamps (also very good quality) at my local IKEA. Price is of course higher than the usual crap sold online, still they’re a lot more convenient compared to well known branded ones.

    2. Anything sold in a brick-and-mortar store or directly by a company based in your home country who thus have more skin in the game if something they sell burns your house down.

      Amazon’s cop out is the whole B2B thing, so you’re not really buying dangerous goods from Amazon, you’re buying them from a random 3rd party in China.

    3. I’m thinking the best bet is to skip the little wallwart dongles and go for something in a larger box which has a power cord instead of sticking right into the wall.

      No, I’m not saying that alone will guarantee a good one. But expecting decent separation between the high and low voltage sides and all the “optional” safety features in a case so small you can fit them side by side on the typical wall socket or power strip…

      Well, maybe if the case is blue and says “Police public call Box” on the outside!

      1. No such luck. My 3d printer came from a us based company with a 100W 12V power supply, that eventually started buzzing noisily. Opening it up, I found on the output a radial capacitor on its side, glued it to the board, but the leads were too short to reach the pcb, so they soldered extensions to it. The solder joint had broken and it was arcing inside. Luckily I knew what it sounds like, having encountered something like it before! A quick tap with the iron fixed the poor solder job.

  1. Just buy from reputable companies and don’t cheap out too much. At least buy Anker or Ugreen if buying “chinese”. There’s “China doesn’t care if you die” and “The good Stuff but much cheaper than any NAME BRAND” stuff. Don’t put your expensive devices or your life at risk over $/€ 5 or 10 more….

    1. The question is,when does Anker/Ugreen/etc decide to ditch quality components/designs, and switch to cheap mass-marketed cruft like these? Will you have any warning when they do so?

      Many corporations before them have gone down that road. Many more will do so.

      1. At least not until now… And those more popular brands are closely tested in (online) magazines, too.
        I checked Amazon.de (and Aliexpress) for the “BK-380 Quickcharge 3.0” device. Amazon doesn’t even have those, at Aliexpress theres one or two sellers for <4USD a piece.

        And those "original Apple form factor" slim chargers were and are always fake and dangerous.

      2. I had a Dell XPS M1330 with an NVidia chip that had a serial manufacturing defect and whose overheating fried two HDDs before it finally died… It had other subpar components as well, I remember the audio card being from a manufacturer that had gone bankrupt and no driver updates for newer OS’s were available. Around that time, Dell was fined for this practice but, if I’m not mistaken, not for this NVidia crap but for bad capacitors in PCs – which is the same business philosophy but that was one case when they didn’t get away with it.

  2. Big Clive made a video about the same topic and was very impressed with the quality of the IKEA chargers – well designed, decent production quality and with 2,50 € for the 5V / 1A version ridiculously cheap…

        1. And put a stamp or logo on it so the Chinese can copy the stamp or logo.

          Example – I needed a battery charger for my camera. I can get cheap mains voltage ones from China. Instead I buy a cheap USB powered charger from China and plug it in to a main to USB 5Volt adaptor that has been certified and purchased in my own country.

          Sadly we have lost lives here because our main is 240V and the Chinese products just modify 110V units without increasing creepage clearance or conformal coatings.

          So if you in the US then don’t buy from a business that you can’t sue. A sad aspect of corporate culture there.

          Anywhere else look for electrical testing conformity certification and look carefully that they are not fake.

          Some marking just mean that the company has purchased a licence for the logo and some makings mean that random samples have been tested and unfortunate some marking are just copied illegally and no compliance has been taken.

          The most trusted marking is not necessarily the one for you particular country. And if you avoid “Made in China” altogether then you are highly likely to avoid fakes.

          These certification systems don’t change often so it is worth some research to find a certification process that you are confident in as most markets are international and carry multiple certification or licence approvals.

          I have had lots of thing brought to me. One was child’s night-light that emitted a smell. When the parents asked me about it after I had opened and inspected it I simply told them that their vigilance saved their child’s life and potentially their own.

    1. I disagree, consumers expect goods to be produced to a standard that says “at a minimum I will be a decent charger and not burn the house down”.

      Retailers in the US/UK/EU should bear some responsibility for ensuring their goods meet local standards (or are very conspicuously labelled to indicate they don’t). Selling through Amazon for instance lends a certain legitimacy to a product “oh I got it on Amazon it must be okay”.

      Price should not be a discriminator for quality – all that does is tell the scammers they can charge more.

      1. This is why I find that practice abhorrent. Sure, I canbuy a charger, but wouldn’t you want to provide a charger that won’t destroy your product or burn down your customers house? Charge them an extra .5% and make everyone happy. Or cut your profit slightly, God forbid.

  3. Back about 60 years ago my dad bought a 9 volt “battery eliminator”.
    A plastic case with a ac cord it was obviously too small for a transformer and switch mode supplies were refrigerator size if they existed at all at that time.
    As it turned out the supply used the impedance of a series capacitor to reduce the voltage followed by a rectifier diode zenier and filter cap. Scary but it worked and still does.
    I haven’t seen any USB chargers use this design but if cheap is the goal it still could happen.

    1. Those designs could never be used for chargers as there’s no isolation between the AC mains and the output; plug it the wrong way and you get live AC on the USB plug shield.
      Those designs can only be used to power fully enclosed devices, where there’s no way for the user to touch anything on the inside.

      1. Should never be used. The subject here being how cheap can you go. A switcher isn’t necessarily isolated either. I’ll have to check if my infamous 9v device is isolated. The plug isn’t polarized. Maybe I am already dead.

      2. It used to be common practice to tie hot to chassis and neutral to chassis with a pair of small capacitors. Yep, the ungrounded chassis would be floating at half line voltage. Last device I know that had this was an old VCR with a metal chassis. Got a nice buzz every time I touched it! No, it did not have a 3-prong cord, just a 2-prong cord.

  4. Legally… by code… in North America, anything that connects to the utility grid must have an electrical approval mark… ETL… UL, CSA, etc. from a recognized lab. The Aliexpress wall warts are noticeably lighter and have only CE mark, which is a self-certification declaration (good luck with that). Considering the quality… that CE could mean for China Export… ;-) only.

  5. My bank was handing out free iPhone looking chargers with their brand on it and it fried my iPhone at the time and I went to their corporate office and threatened to see them and they gave me the money to buy a brand new one.

    1. AFAIK all USB 5V power supply chips come with a reference implementation. You can just build that. But then you need to spend the engineering effort to build proper clearances in to prevent arcs from crossing directly from the high to low voltage sides. You need to spend the money to buy the triple insulated transformers (two layers of enamel plus a third layer of plastic to insulate the transformer windings). Spend money, time, and effort to send your product off for proper testing and certification. Do all of that, and your product is no longer $1.

  6. This tear-down goes a long way to explain why the PoS cheap chargers last quite a while charging phones (often at degraded power), but go soft when used in continuous duty eg. powering a Pi.

    1. Belgian firefighters have warned several times on Belgian TV about the increase in house fires due to USB chargers. They also did it several years ago when hoverboards were in vogue, about house fires caused by cheap hoverboards intgratting dangerous batteries.

    2. I hear more about deaths in my country as the mains here is 240V.

      That’s probably because we have better regulations but not well enough enforced. A death from fire is still unacceptable failure.

  7. A lot of modern chargerd have no filtet capacitors ot chokes on the mains input so create onterference and noise that cause problems with radio or wifi reception i remember many computet powet supplies used in bbc computet and vdu tetminals have a 220 mgd capacitir next to a hot hestsink so they fail and nolia computet monotord used to catch fire the power supply would burn out you cant best a resl trandformer power supply witj linear regulator

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