Three different wattages can all be correct
A charging setup has at least three relevant limits: what the charger can offer, what the cable can carry, and what the Mac is prepared to request. The lowest applicable limit constrains the connection.
Even after negotiation, the Mac controls the moment-to-moment draw. Battery charge level, temperature, system load, Optimized Battery Charging, and the normal taper near full all affect how much power moves into the battery.
Negotiated power versus live battery power
Negotiated power describes the power profile agreed between the charger and Mac. Live battery power describes what is entering or leaving the battery now. They are related, but they should not be expected to match.
The Mac may negotiate with a 96W charger while the battery receives far less because the battery is nearly full or the computer is using part of the incoming power.
When is a charger actually undersized?
A charger is clearly undersized when its advertised capability is well below what the Mac can use for fast charging. A small phone charger connected to a MacBook Pro is one example. That judgement should be based on the charger's capability, not on one slow sample during an overnight charge.
WhatBattery Pro's charging sessions show how every session ran. On supported 14-inch and 16-inch MacBook Pro models, they also show whether the charger's advertised wattage falls short of the Mac's fast-charge capability.
Why power can be negative while connected
If the charger cannot cover the computer's current load, the battery may still discharge while the cable is connected. A weak charger, a cable or hub limit, or an intensive workload can all contribute. Seeing live battery watts makes that state explicit.
A better way to test a charger
- Start with the battery below full, so charging is not already tapering.
- Connect the charger directly where practical.
- Check the negotiated charger capability.
- Watch live input and battery power over more than one moment.
- Compare the result with the Mac's supported fast-charge setup.