Quick answer: A USB-C connector carries power on VBUS and ground, and it can deliver 15 W by default, 100 W at 20 V and 5 A with USB Power Delivery, or 240 W at 48 V with extended power range. The voltage is not fixed by the connector: the charger and the device negotiate it over the configuration channel, and the cable has to declare its current rating with an e-marker. Plug in a cable without one and the link falls back to 3 A, so a 100 W charger delivers at most 60 W.
The connector itself is rated for 5 A per contact set and for a limited number of mating cycles, so the electronics and the cable are what limit a real system. Understanding the three numbers, voltage, current and cable rating, explains why the same laptop charges at different speeds from three chargers that all look identical.
The pins that carry power
VBUS, ground and the pairs
A USB-C plug has 24 contacts. Four carry VBUS, four carry ground, and the rest handle SuperSpeed pairs, the configuration channel, sideband use and USB 2.0. VBUS and ground are duplicated so the connector can pass high current without overheating a single contact, and the plug is reversible because the two rows mirror each other.
CC decides everything
The configuration channel is a single wire in each direction. The charger advertises its capabilities, the device requests a voltage and current, and both agree before VBUS rises above 5 V. Without a valid CC handshake, a USB-C port stays at 5 V, which is why a damaged CC pin turns a fast charger into a slow one.
Voltage, current and cable rating
| Tier | Voltage | Current | Power |
|---|
| Default | 5 V | 3 A | 15 W |
| PD fixed | 9, 12, 15, 20 V | Up to 5 A | 100 W |
| PD PPS | 3.3 to 21 V in steps | Up to 5 A | Adjustable |
| EPR | 28, 36, 48 V | Up to 5 A | 240 W |
| Cable without e-marker | Any | 3 A limit | 60 W at 20 V |
Why the same charger behaves differently
Three things can cap the result. The cable may lack an e-marker, so the charger refuses to go beyond 3 A. The device may request a lower profile because its battery is warm or nearly full, which is normal thermal management. Or the port may be a data-only implementation that never enables VBUS above 5 V, which happens on some hubs and monitors.
Watts printed on a charger are its maximum, not a promise. A 100 W supply feeding a phone that asks for 25 W delivers 25 W, and the rest is headroom. Conversely a 45 W supply feeding a laptop that wants 90 W will run at 45 W and may not charge while the machine is busy, which users often interpret as a faulty cable.
Connector durability and safety
The connector is rated for about 10,000 mating cycles, far fewer than the USB-A design it replaces, and the small contacts are sensitive to lint and to leverage. A cable hanging from a laptop port puts a bending load on the shell; use a right-angle plug or a short tail where the port is vertical. Heat is normal at 100 W, but a plug too hot to hold means contact resistance, usually from contamination or a worn socket.
For a desk that charges and drives a display, choose a cable rated for both current and data: a Type-C hub passes only what its upstream lead supports, and a USB-C extension cable re-negotiates the e-marker, which can silently drop 100 W to 60 W. Where the host is USB-A, the USB-A extension cable route cannot deliver more than 15 W at any length.
Practical scenarios
- Laptop that charges slowly on a 100 W brick: swap the cable for one marked 5 A, then check the port’s reported wattage; if it stays at 60 W, the cable was the limit.
- Phone on a laptop port: expect 15 W at best, because a data port rarely implements high-voltage profiles for peripherals.
- Powered speaker or mini PC with a C input: confirm the device expects PD rather than a fixed 12 V barrel; a PD supply set to 20 V will not boot a device designed for 12 V.
- Long cable run to a wall socket: keep the PD lead under 2 m and put the length in the mains side, where loss does not affect negotiation.
FAQ
Can any USB-C cable carry 100 W?
No. It needs an e-marker declaring 5 A and conductors thick enough to carry it. Cables sold as charge-only are usually limited to 3 A, and some thin leads are rated lower. The charger cannot exceed the cable’s declaration, so the cable decides the ceiling.
Is 240 W safe on a phone?
Yes, because the device requests what it can accept. A 240 W supply and a phone negotiate 5 V or 9 V at a low current; the higher voltages only appear when the device asks for them. The risk is a non-compliant charger that ignores negotiation, which is why certified hardware matters.
Why is the plug warm?
Some warmth is normal at high current because the contacts have resistance. A plug that is uncomfortable to hold, or that discolours, indicates a poor contact, a damaged cable or a worn socket. Stop using it and replace the cable before the port is damaged.
