Troubleshooting
Why won't your MacBook charge at full speed?
· Cablyst
Your MacBook says "Not Charging," or the battery creeps up while you're using it, or a charger that's supposed to be 96 W is trickling in 30. Slow charging feels random. It almost never is. It's a Power Delivery negotiation that settled lower than you expected — and one of three things capped it.
The three suspects
1. The cable. This is the most common and the most invisible. A USB-C cable rated for only 3 A tops out around 60 W no matter how good your charger is. Many bundled and cheap cables are 3 A. A 100 W charge needs a 5 A e-marked cable; 140–240 W needs a 5 A EPR cable.
2. The charger. A charger advertises a set of power profiles (PDOs). If none of them match the voltage/current your Mac wants, you get the next one down. A "65 W" charger shared across ports often drops to 45 W or less when something else is plugged in.
3. The port / conditions. Thermal limits, a busy hub, or a port wired for data-only can all reduce the contract.
How to actually diagnose it
Guessing which of the three it is — by swapping cables and chargers — is slow and inconclusive. The negotiation itself is the evidence, and macOS exposes it.
Cablyst reads the negotiated PD contract (the exact volts and amps agreed) and every power profile the charger offered, per port. In one screen you see whether:
- the charger never offered a high-wattage profile → charger's fault;
- the contract is capped at 3 A while the charger offered 5 A → cable's fault;
- everything's on offer but the contract is throttled → conditions.
Stop swapping cables. Read the contract.
The 30-second version
Plug in, open Cablyst, look at the port. If the cable line says 3 A and you wanted 100 W, you found it. If you want to confirm before buying anything, the PD Contract Inspector in Cablyst Pro shows the full negotiation and every offered PDO.
Want the real, hardware-level answer for your own cable? Install Cablyst or get Pro ($9.99 lifetime).