A product gets a drawing, a bill of materials, a tolerance discussion and a sample review. Its cable gets a line saying « cable, black, one metre ». Its power supply gets a line saying « adapter, EU plug ». Then the finished product is the thing that carries a mark, a warranty and your name on it. The mismatch between the attention given and the risk carried is nowhere wider than here.
Why these parts fail more than the product does
Three reasons, and they compound. They are the parts the user handles most, so they take mechanical abuse the product never sees. They are sourced on price by whoever assembles the finished goods, often without telling you, because nobody wrote down what they had to be. And they are the parts a market surveillance authority can test without opening anything: a plug, a cord and a power supply are checkable on a bench.
The consequence is that a product can be entirely conforming and still be refused, recalled or returned because of an accessory that cost a fraction of it. Worse, the accessory is usually the part that was changed silently between the sample and the series, because it was the easiest place to find margin.
What to write down for a cable
- The real conductor cross-section, and how it will be verified. A cable can be printed with one section and built with another; the only honest check is a cut sample and a measurement.
- Copper, and what kind. Copper-clad aluminium exists, is cheaper, and behaves differently in heat and in flexing. It is not a fault in itself — it is a fault when it arrives without being asked for.
- The insulation material and its temperature rating. Two cables that look identical can be rated for different environments.
- Shielding, if the product needs it. Whether it is braid, foil or both, and whether it is actually connected at each end.
- The strain relief at each end. Overmoulded or assembled, and tested by pulling — this is where a cable dies.
- Length, colour, marking and packaging. Trivial until the box will not close or the marking contradicts the manual.
A power supply is a certified object, not an accessory
The power supply is the component most likely to sit in a regulated category on its own, with its own safety standard, its own test report and its own marking obligations. For a great many electrical and electronic products the applicable safety standard is IEC 62368-1 and its European version; which standard applies to your case depends on the product, so confirm it against the text rather than against a supplier's summary.
What you ask for is a certificate that names the manufacturer and the exact model, with a test report behind it, and the ability to check that certificate at the body that issued it. The IECEE CB scheme exists precisely so that a report can be recognised across countries. A PDF with a logo is not a certificate; a certificate you cannot find in the issuer's own database is worth asking about before it is worth believing.
Certificates are issued for a model, not for a factory. A supplier who sends you a valid certificate for a model that is not the one in your box has not lied to you and has not covered you either. Check that the model number on the certificate is the model number moulded on the part in your hand.
Marking is part of the product, not of the packaging
A power supply carries information that has to stay readable for the life of the product: the manufacturer's identification, the model, the input and output ratings, and the conformity markings that apply to it. European rules also require identification of the responsible economic operators — who exactly, and on the product or on the packaging, depends on the product legislation covering your category, which is worth checking in the text rather than assuming. What is never acceptable is a marking added by a sticker that survives neither a thumb nor a summer.
The trap of « same as sample »
« Same as sample » feels like the safest instruction in sourcing and is one of the weakest. It only works if both sides hold the same sample, if the sample is sealed and signed, and if everyone agrees on which of its properties are being referenced. None of that is true by default. In practice, the phrase means « same appearance », and appearance is the one property of a cable or a power supply that says nothing about how it will behave.
| What you ask for | What it proves | What a weak answer looks like |
|---|---|---|
| A cut section of the cable, kept by both sides | The real conductor and its section, verifiable later | « Standard specification, don't worry » |
| The certificate number for the exact power supply model | That this model was tested, by a body you can contact | A picture of a certificate for another model of the same family |
| The name of the actual maker of the accessory | Who you are depending on, and whether they can be qualified | « Our partner factory », with no name |
| Written notice before any change of accessory supplier | That a silent substitution becomes a contractual breach | Agreement in conversation, nothing in the order |
None of this requires a laboratory or a large budget. It requires writing three or four lines into the purchase order that today are not there, and keeping one sealed sample of each accessory. The cost of that discipline is an afternoon. The cost of skipping it is a shipment you cannot sell and cannot send back.