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I am about to wire up this power supply to my mains voltage via a flippable plug (Schuko.)

https://www.az-delivery.de/en/collections/stromversorgung/products/copy-of-220v-zu-5v-mini-netzteil

Its AC pins are labelled AC/N and AC/L but since my project will be connected via a Schuko-plug, I can not guarantee that those will always be correctly connected and not mixed up.

What is the worst thing that can happen if N and L are mixed up?

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The data sheet for the power supply module shows this circuit that I've red-lined: -

enter image description here

I would be interested in ensuring that the two capacitors in the red box were Y1 \$\color{red}{\text{(amended)}}\$ rated and that there are sufficient clearances across the red line inside the module before using it. I would naturally assume that these things are in order on normal supplies from Traco, XP, Murata (i.e. the usual people who sell these things) but, there is nothing on your link about the quality of the goods you have bought so, do some homework and find things out. When your mind is rested on these things and everything looks in order then you can connect L and N either way round.

What is the worst thing that can happen if N and L are mixed up?

Electrocution if the module is made by some back-street outfit who don't know what they are doing so, do your homework and prove to your own satisfaction that they have a QA system that meets ISO 9000.

To me, they look dodgy and I wouldn't touch them with a barge-pole wired either way round but, you might have "insider" information that I don't have.

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  • \$\begingroup\$ Thanks for the detailed answer. Unfortunately there is no further information on the device itself or in the packaging other than what is in that datasheet. \$\endgroup\$
    – clamp
    Commented Sep 25, 2021 at 13:24
  • \$\begingroup\$ I wouldn't use it on that basis. \$\endgroup\$
    – Andy aka
    Commented Sep 25, 2021 at 17:52
  • \$\begingroup\$ "... that the two capacitors in the red box were X1 rated" - Shouldn't they be Y-rated (short poses shock hazard) instead of X-rated (short poses fire hazard)? \$\endgroup\$
    – marcelm
    Commented Sep 27, 2021 at 9:30
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    \$\begingroup\$ @marcelm absolutely correct. I shall amend my brain-fart. \$\endgroup\$
    – Andy aka
    Commented Sep 27, 2021 at 9:54
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Electrocution is your downside... but no need to leave that to chance.

It's perfectly possible to obtain power supplies which have been certified as safe by Recognized Testing Labs. For instance Underwriter's Laboratories' "gold standard" mark that is vigorously defended and rarely counterfeited, is the "ЯU" mark. It is the equivalent of the "UL Listed" mark, except this mark is for components. There are several other recognized labs, such as TUV, BSI, SGS, etc.

Unfortunately the CE mark is poorly defended and universally counterfeited. The only way the CE mark can be trusted is if purchased inside the EU and you have reliable chain of custody from an EU manufacturer. (importer will suffice if they are a reputable company with a substantial bricks and mortar presence in the EU; i.e. a lot to lose from an enforcement action, such as Siemens).

Of course your item came direct mail from a site that markets to hobbyists, so it is essentially guaranteed to be Chinese schlock with a faked CE mark that has actually never seen the inside of a testing lab.

Anyway, quality power supplies which have been vetted by a recognized testing lab are commodity items readily available. Just use one of those.

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