Why this answer matters
A charger can be electrically compatible without delivering the phone's fastest supported charging mode. Separating basic compatibility from maximum charging speed prevents unnecessary charger replacement.
4 requirements4 verification steps1 primary source
Requirements
What has to be true
- USB-C power for wired charging.
- 20W or higher USB-C adapter for Apple's stated wired fast-charge test condition.
- For up to 25W MagSafe wireless charging, Apple specifies a 30W-or-higher adapter with the supported MagSafe charger.
- Cable, charger, temperature, battery state and active use can reduce real charging speed.
Verify it yourself
Use this test sequence
Change one variable at a time so you know which requirement made the difference.
- 1
Confirm the adapter output rating instead of relying on its physical size.
- 2
Use a known-good USB-C cable and remove questionable hubs or extensions while testing.
- 3
If charging is intermittent, compare the same phone with another known-good cable and adapter before blaming the USB-C port.
- 4
Use DeviceOK's wattage matcher to compare the adapter rating with the device requirement you are trying to meet.
Limits
What this answer does not prove
- A browser cannot read the phone's negotiated USB Power Delivery wattage directly.
- Apple's fast-charge figures are test-condition results, not a promise that every charge session will sustain the maximum rate.
Relevant DeviceOK checks
Test the part you can observe
Charger Wattage MatchCompare a device's entered power requirement with a charger's rated wattage while keeping USB-PD/PPS and voltage-profile limits explicit.
→USB-C Cable Power Rating CheckCompare an entered cable wattage rating with the power you want to carry, while keeping protocol/e-marker limits explicit.
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