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01A chip that speaks for the cable
An e-marker USB-C cable has a small chip, usually in one or both plugs, that tells the charger and the device what the cable can handle: its maximum current, maximum voltage and data speed. It exists so a charger never pushes more power through a cable than the wires can safely take.
A USB-C charger can't see the copper inside a cable. A thin, cheap cable and a thick, well-made one look identical from the port. So the USB-C standard plays it safe: unless the cable proves otherwise, the charger assumes it can handle 3 amps. At 20 volts, that's 60 watts. To go above 3A, the cable has to carry an e-marker that says "I'm rated for 5A."
E-markers also appear in faster data cables. Full-featured USB-C cables (USB 3.x, USB4 and Thunderbolt) carry one so the devices at each end know which speeds the cable supports.
You'll never see the chip. It's built into the plug housing, and the cable looks and feels like any other. The only outward clues are the rating printed on the packaging and, on better cables, a small marking on the plug itself.
02What happens when you plug in
- You connect a USB-C to USB-C cable between a charger and a device.
- The charger powers the e-marker chip through a spare pin in the plug and asks the cable to identify itself.
- The chip replies with its ratings, for example 5A and 50V (the label for 240W cables).
- The charger and device negotiate a power level through USB Power Delivery, capped by whatever the cable reported.
- No reply means no e-marker, so the charger caps current at 3A however powerful it is.
Watts = volts × amps. 20V × 3A = 60W. 20V × 5A = 100W. 48V × 5A = 240W.Every jump above 60W needs 5A, and 5A needs an e-marker.
This all happens in a fraction of a second, every time you plug in. The USB Power Delivery explainer goes further into how charger and device agree on a voltage, and watts, volts and amps covers the basic math.
03Do you need an e-marker cable?
| Device and charging mode | Power needed | E-marker cable needed? |
|---|---|---|
| Any iPhone with USB-C | Well under 60W | No |
| Google Pixel phones | Under 60W | No |
| Galaxy phones at 25W (Super Fast Charging) | 25W | No |
| Galaxy Plus and Ultra models at 45W | 45W at 5A via PPS | Yes |
| Galaxy S26 Ultra at 60W | 60W at 5A via PPS | Yes |
| iPad and small laptops | Up to 60W | No |
| Laptops over 60W | 65W to 100W | Yes, 100W or 240W cable |
| Gaming and workstation laptops | Up to 240W | Yes, 240W cable |
The Samsung rows catch people out. A 45W charge sounds like it fits inside a 60W cable, but Samsung's PPS modes run at roughly 10V and up to 5A, so the current is the limit, not the watts. With a 3A cable, the phone falls back to 25W and you'll never see "Super fast charging 2.0" on screen. Our Samsung fast charging guide has the full checklist.
One subtle point: the charger has to support the higher power too. A 5A cable plugged into a 25W charger still charges at 25W. The cable removes a ceiling, it doesn't add power. For a Galaxy at 45W you need three things together: a phone that supports it, a 45W PPS charger, and a 5A cable.
04How to tell if your cable has one
No marking at all? Assume it's a 3A cable. It will still charge everything; it'll just cap laptops and Samsung's top modes. That's no problem for an iPhone or Pixel.
Some cheap cables claim 100W without an e-marker inside. They're not dangerous, because the charger will just limit them to 3A, but you won't get the speed you paid for. A power meter or the Samsung on-screen message is the quickest way to check.
05Is a 5A cable worth buying anyway?
If you have a Galaxy Plus or Ultra, or a laptop that charges over USB-C at more than 60W, yes. It's the cheapest upgrade that makes a visible difference. Even if you only own an iPhone, one 100W or 240W cable in the bag means you can borrow a friend's laptop charger, top up a tablet or charge a work laptop without hunting for the right lead. Pair it with a charger that has the wattage to match, like a multi-port GaN brick; see can I use my laptop charger for my phone.
Rated 100W and 240W, so they carry the 5A that laptops and Samsung's fastest modes need.
Questions people ask
What does e-marker mean on a USB-C cable?
It means the cable contains an electronically marked chip that reports its current rating, voltage rating and data speed to connected devices. It's what lets a USB-C cable carry 5A, for 100W or 240W charging.
Do I need an e-marker cable for my iPhone?
No. iPhones charge at well under 60W, which any standard 3A USB-C cable handles. An e-marked cable works fine with an iPhone too, it just won't make it charge faster.
Is a cable without an e-marker unsafe?
No. A charger treats any cable without an e-marker as a 3A cable and limits current to match. You get up to 60W, safely. The risk is a cable that falsely claims 5A, which is why the chip exists.
Does a 240W cable have an e-marker?
It should. Every USB-C cable rated above 60W needs one, because it must carry 5A. Certified 240W cables are marked for 5A and 50V, which supports the 48V Extended Power Range in USB PD 3.1.
Can a USB-A to USB-C cable have an e-marker?
Not for 5A charging. E-markers and USB Power Delivery's higher power levels work over USB-C to USB-C cables. A USB-A to USB-C cable can't negotiate USB PD, so it can't reach 100W or 240W.