How to Buy a Phone Cable Safely
Why is it worth checking a cable before buying?
A phone cable looks like a simple wire, but it carries power into a battery and signals that tell the phone and charger how much current is safe. Wikipedia documents USB-C cables built with the wrong resistor value on a signalling pin, which led devices to misjudge how much power was available, and records cases of damaged chargers, ports and even laptops. A good cable costs a little more than a bad one. Replacing a damaged phone costs a lot more.
What certification should I look for?
The USB-IF reminds consumers to purchase compliant USB products from trusted sources that display USB-IF certified logos on packaging, in product briefs or on the cable or device itself (source). Certification is meant to show the product was tested against the standard. It does not mean the product is the best one for your phone.
Can safety marks be faked?
Certification marks are worth looking for, but counterfeiters copy them. In November 2020 UL warned that two models of USB charger carried counterfeit UL marks and had never been evaluated by UL for the risk of fire, electric shock or injury, and told users to stop using them. The lesson is to pair marks with a trustworthy seller.
The danger of uncertified electronics is real. In December 2017, Electrical Safety First tested 50 counterfeit and lookalike iPhone chargers bought in the UK. It reported that 49 failed safety tests, that 46% failed the electrical strength test meant to prevent shocks, that 46% had substandard components or spacing inside, and that 15 had plug pins that could break off and stay in a socket. Those were chargers, not cables, and the sample was small, but the advice from the charity applies to both: buy directly from trusted retailers.
How do I match the cable to the job?
Power ratings matter. The USB-IF says USB Power Delivery was limited to 100W using cables rated at 5A before revision 3.1, and that 240W needs updated cable requirements (source). Wikipedia sets out the steps:
| Cable rating | Power available | Good for |
|---|---|---|
| Standard USB-C cable (3A at 20V) | Up to 60W | Phones and tablets |
| 5A-rated cable (5A at 20V) | Up to 100W | Many laptops |
| Extended Power Range cable (5A at 48V) | Up to 240W | The most powerful laptops and devices |
Check the wattage you need in the wattage guide, and see USB Power Delivery for how the standard works. For data, a cable also has a speed. See USB 2.0 vs USB 3.x.
Follow your manufacturer
Apple says you might not be able to charge an iOS device with USB-C power adapters that are not made by Apple (source). Samsung says to use only Samsung-approved charging devices and that other accessories may invalidate your warranty and cause damage (source). For Apple’s Lightning connector there is an extra layer: Wikipedia says Apple’s MFi program gates accessory quality, so an MFi-approved cable is the safer choice. See Lightning.
What are the warning signs of a bad cable?
This checklist is ours, built from the advice above:
| Warning sign | Why it matters |
|---|---|
| No brand, no model number, no certification on the packaging | Nothing to check, and nobody accountable |
| A price far below every trusted brand | Corners may have been cut on parts or testing |
| A seller you cannot identify | Counterfeits spread through anonymous listings |
| No stated wattage or speed | You cannot tell whether it suits your phone |
| A safety mark you cannot verify | Marks can be forged, as UL’s 2020 warning shows |
| Cable or plug runs hot while charging | Stop using it |
| Loose plug, bent pins or exposed wire | Replace it, do not tape it |
A simple buying checklist
- Check the logo or certification, not the price tag.
- Check the connector: USB-C or Lightning.
- Check the wattage and speed rating against what your phone can use.
- Buy from the phone maker or a retailer you trust.
- Keep the receipt in case the cable fails.
- Read the full charger safety guide.