USB-C Power Delivery Explained
USB-C Power Delivery (USB-C PD) is the protocol your Mac and charger use to negotiate how much wattage to send over the cable — up to whatever maximum both the charger and cable support. Your Mac requests only what it needs at any given moment, so a higher-wattage charger never forces extra power in, but a charger or cable that tops out lower than what your Mac is asking for will hold back charging speed.
How the negotiation actually works
When you plug in, your Mac and the charger use the cable's data pins to exchange a list of wattage/voltage combinations each side supports, then agree on the highest one both can handle. This isn't a one-time handshake — the negotiated wattage can change while you're plugged in, dropping as the battery approaches full, or rising again if you start a demanding task like a video export while the battery is low.
What wattage does your Mac actually need?
Apple ships different chargers with different Mac models because the power draw varies:
- MacBook Air — typically ships with a 30W–70W charger, depending on model and configuration.
- 13/14-inch MacBook Pro — typically 67W–96W.
- 16-inch MacBook Pro — typically 96W–140W, especially for higher-end chip configurations.
As a rule of thumb, matching or exceeding your Mac's original charger wattage guarantees full-speed charging, including while the Mac is under heavy load. A lower-wattage charger will still charge the Mac — just more slowly, and it may lose the race against battery drain if you're running something demanding while plugged in.
Why the cable matters as much as the charger
Power Delivery wattage is capped by whichever is lower: the charger's maximum, or the cable's rating. A 140W charger connected with a cable only rated for 60W will negotiate down to 60W — with no error or warning from macOS. See Why Is My Mac Charging Slowly? for how to tell whether a cable is the bottleneck.
Common Power Delivery myths
- "A higher-wattage charger will overcharge or damage the battery." False — the Mac controls the negotiation and only ever draws what it needs.
- "Any USB-C charger works with any Mac." True for charging at all, since Power Delivery is a USB standard, not an Apple-specific one — but charging speed depends entirely on the charger and cable's actual wattage rating.
- "Third-party chargers are inherently worse." A properly PD-compliant third-party charger rated for sufficient wattage performs the same as Apple's own. Quality varies by manufacturer, not by being non-Apple.
How to check what wattage your Mac is negotiating right now
- Open System Information (hold Option and click the Apple menu → System Information).
- Select Power in the sidebar.
- Look at AC Charger Information for the negotiated wattage.
WattsConnected shows this same number live in the menu bar, so you don't need to open System Information every time you plug in — and it flags the moment a charger or cable is negotiating less than your Mac is capable of using.
Frequently asked questions
Does a higher-wattage charger charge my Mac faster?
Only up to the wattage your Mac is actually able to draw. USB-C Power Delivery negotiates the wattage between your Mac and the charger, so your Mac requests what it needs rather than accepting everything a charger can supply. A 140W charger won't charge a MacBook Air any faster than a 70W charger, but it will help a 16-inch MacBook Pro reach full charging speed under heavy use.
Can I use a 100W charger on a MacBook Air that came with a 30W charger?
Yes. USB-C Power Delivery chargers are backward compatible — your Mac will only draw the wattage it needs, so a higher-wattage charger is always safe to use. It won't charge a MacBook Air any faster than its own charger, since the Mac itself caps the request.
Can I use a 30W charger on a Mac that came with a 100W charger?
Yes, it's safe, but it will charge more slowly and may not keep up at all if you're using the Mac heavily while the battery is low — the charger simply can't supply as much as the Mac would otherwise draw. It's fine for topping up overnight or light use, but it's not a substitute for the original charger's wattage during demanding work.
Is it bad to use a non-Apple USB-C charger with a Mac?
No, as long as the charger is USB-C Power Delivery compliant and rated for enough wattage. The negotiation protocol is a USB standard, not an Apple-specific one, so third-party PD chargers work the same way Apple's do — the difference shows up only if the charger or its cable can't supply the wattage your Mac is asking for.
See also: Is My Mac Getting Enough Power From My Charger? (Decision Tree)