When a router suddenly dies, many people assume the router is broken. Yet the part that fails most often is its power adapter, a small box that runs warm for years and takes a power surge every time the mains cut out and come back.

Signs of a failing adapter

  • The router powers on and off repeatedly, especially when many devices are connected.
  • The indicator lights are dim or flicker oddly. What normal lights mean is covered in the guide to router indicator lights.
  • The router only stays on when the adapter cable is wiggled or bent a certain way.
  • The adapter buzzes, smells burnt, or is too hot to hold.
  • The router won't power on at all, but works normally with another adapter of the same specification.

The easiest confirmation is the last point: borrow an adapter with exactly the same figures and try it.

Reading the adapter label

Look at the OUTPUT section of the old adapter's label, or under the router near the power socket.

  • Voltage (V): must be exactly the same. A 12 V router given 9 V will cycle on and off; given 19 V it can be permanently damaged.
  • Current (A): the replacement must be equal or higher. A 12 V 1 A router is safe on a 12 V 1.5 A or 2 A adapter.
  • Polarity: a small circle symbol with + and − marks. Almost all routers use centre positive. Reversed polarity can destroy a router instantly.
  • Plug size: most commonly 5.5 × 2.1 mm or 5.5 × 2.5 mm. A loose plug causes intermittent power.
  • DC or AC: some older devices use AC output. Make sure the type matches.

Choosing a replacement

  • Prefer the router brand's own adapter or a branded adapter with a national safety certification mark.
  • Avoid very light, very cheap unbranded adapters; many can't deliver the current printed on them.
  • Avoid "universal" adapters with a voltage dial. They are easily nudged to the wrong setting.

Making adapters last longer

  • Keep the adapter somewhere with airflow, not buried behind a cupboard or under a mattress.
  • Use a surge-protected socket, or a small UPS that also keeps the internet running during outages, see the guide to a UPS for your router.
  • Don't bend the cable right at the base of the plug; that is where it most often breaks inside.

If the router still cycles on and off with a new adapter, overheating may be the cause. Check the guide to an overheating router.

Before buying a new router, suspect the adapter. A replacement must have the same voltage, the same or higher amps, the same polarity, and a plug that fits. All three figures are already printed on the old adapter's label.

Frequently asked questions

Can I use an adapter with a higher amp rating?

Yes. As long as the voltage and polarity match, a higher-amp adapter is safe because the router only draws the current it needs. A different voltage or a lower amp rating is what to avoid.

Can I replace the adapter of a provider's modem myself?

Technically yes, but if the device still belongs to the provider, report it to customer service first. A faulty adapter is usually replaced free of charge as part of the equipment rental.

Can a router be powered from a USB port or power bank?

Only if the router is designed for 5 V. Most home routers use 9 or 12 V, so you need a USB-to-12 V step-up cable that meets its current requirement.