USB-C Charger Buying Guide: Watts and Safe Cables

USB-C charger buying guide rule one: match the charger to the device, then buy a charger and cable that carry a real certification mark. A phone, a tablet and a laptop all use the same oval plug, but they do not need the same power.

Start with watts, not the plug

Watts measure how fast a charger can deliver power. A small phone may need about 20 watts to charge quickly. A thin laptop often wants 45 to 65 watts. A larger laptop can ask for 100 watts or more.

Look for the wattage on your old charger. It is printed in small type on the brick, often as volts times amps. Multiply them if the watts are not shown. A 20 volt, 3 amp charger gives 60 watts.

A stronger charger is safe for a weaker device. The device only takes what it asks for. A 65 watt charger will charge a phone without trouble. The reverse does not work well. A 20 watt charger on a laptop may charge very slowly, or not at all while you work.

Buy for your biggest device if you want one charger for everything. Buy for your phone if that is all you charge.

Sources: USB Promoter Group, USB Power Delivery Specification Revision 3.1 announcement, May 26, 2021 (usb.org), for the 100 watt limit that applied before that revision.

What USB Power Delivery means

USB Power Delivery, or PD, is the rule set that lets a charger and a device talk to each other. They agree on a voltage before the power flows. This is why one PD charger can run a phone at one voltage and a laptop at another.

Before May 2021, PD topped out at 100 watts. That used 20 volts and a cable rated for 5 amps. In May 2021 the USB Promoter Group announced Revision 3.1. It reaches up to 240 watts, with new fixed voltages of 28, 36 and 48 volts joining the older 5, 9, 15 and 20 volt steps.

Most buyers do not need that top level. It matters for large notebooks and other high power products. For now, 100 watts covers nearly every laptop, phone and tablet. Check the product page or box for the words "Power Delivery" or "PD" and the output watts.

The group also noted that products in the 100 to 240 watt range face stricter safety rules, set by each country where they are sold.

Sources: USB Promoter Group, USB Power Delivery Specification Revision 3.1 announcement, May 26, 2021 (usb.org).

Choose the right cable

A charger is only half of the setup. The cable sets a limit too. Many cheap cables are built for phones at lower power. They can get warm, or charge slowly, on a laptop.

For 100 watts, the cable must be rated for 5 amps. For anything up to 60 watts, a standard cable rated for 3 amps is enough.

Check the cable label or product page for the amp or watt rating. If it says nothing, treat it as a basic phone cable. The USB Promoter Group said in 2021 that new labels were planned to show the power a certified USB Type-C cable supports. Until you see such a label, read the specs.

Keep cables short and undamaged. A frayed or bent cable is a risk at any price. Replace it rather than tape it.

Sources: USB Promoter Group, USB Power Delivery Specification Revision 3.1 announcement, May 26, 2021 (usb.org).

Avoid unsafe cheap chargers

A very low price on a high wattage charger is a warning sign. Safe power circuits cost money to build. Chargers that skip tests can overheat, or send unstable power into your phone.

Look for a known brand, a model number, the maker name and the safety marks printed on the case. Weigh the charger in your hand. A 65 watt charger that feels as light as a 5 watt one deserves a second look.

USB-IF, the group that runs the USB standards, keeps a public search of products certified to carry its logo. If a product is not listed, USB-IF advises you to ask the maker when it expects certification.

Buy from a shop that offers a return. Stop using any charger that smells hot, buzzes, or shows burn marks, and do not leave one on a bed or sofa while it charges.

Sources: USB Implementers Forum, certified products search (usb.org/products); USB Promoter Group announcement, May 26, 2021 (usb.org).

A short checklist before you buy

Write down the watts your device needs. Pick a charger at or above that number. Choose one that lists Power Delivery. Pair it with a cable rated for the same power, with a 5 amp rating if you need 100 watts. Buy from a seller you can find again.

One good charger and one good cable cost a little more than a bargain pair. They protect devices that cost far more, and they last for years. If a package is vague about watts, certification or the maker, put it back.

Also check how many ports the charger has. When two devices share one charger, the watts are split between them. A 65 watt charger with two ports may give only 45 watts to a laptop once a phone is plugged in. The label usually lists the split.

Sources: USB Promoter Group announcement, May 26, 2021 (usb.org); USB Implementers Forum, certified products search (usb.org/products).

Sources

• USB Promoter Group, "USB Power Delivery Specification Revision 3.1" developer update, May 26, 2021: https://www.usb.org/sites/default/files/2021-05/USB%20PG%20USB%20PD%203.1%20DevUpdate%20Announcement_FINAL.pdf
• USB Implementers Forum, certified products search: https://www.usb.org/products