If you own one of Apple’s portable systems, you will have either a 60-watt or 85-watt power adaptor that comes with the unit for charging it. With these, you can either charge your battery or run the system directly from wall power; however, there are times when these adaptors may not work properly, or at least show behaviors that might be concerning.
After using your adapter for a while, especially if you are charging your system’s battery in addition to running computationally intensive tasks that use excessive processing power, then you may be pushing your power adapter to its capacity.
For the most part, a hot power adapter is nothing to worry about, unless the adapter is not properly ventilated. Just be sure you do not sandwich the adapter between pillows or under books, and it should not get hot enough to be a problem.
Apple’s power adapters include a thermal shut-off switch, that should prevent the adapter from overheating to the point of failure. If the adapter gets too hot to function safely, then it will simply not work until it cools down.
Buzzing noise from adapter
If you hear slight buzzing or clicking sounds coming from the adapter, then again this should not be much to worry about. This is likely just capacitor noise, which occurs with slight heat-generated vibration between the components of capacitors and circuit boards that are subjected to alternating current (wall current). Since alternating current switches direction at about 60Hz, you may hear a buzzing sound at about this frequency, which is a relatively low humming tone but which from the capacitor includes overtones and harmonics that give it a crisper buzzing sound.
Like heat fro the adapter, such noise is nothing to worry about and should not affect the power adapter’s functions.
Adapter not charging
If your power adapter is not charging your system, then there may be several factors at play. The first may be if, as mentioned above, your adapter has become hot to the point where it has shut off. If it is hot to the touch, then let it sit out for a while to cool off, and try using it again.
Beyond heat, Apple’s power adapters will shut off if exposed to excessively noisy circuitry. AC power in wall circuits may have spikes and jumps in voltage beyond the expected ~60Hz oscillations, and sudden surges or drops in voltage can damage some electronics. To check if this is happening with your adapter, try plugging it into a separate circuit, and especially one without many other devices on it. If the adapter works on one circuit and not another, then you may have to have the circuit serviced.
Faulty cabling could be a contributing factor for either the wall jack and cable, or the magsafe cable of your adapter. For the wall cable, you can swap it out with the optional wall plug to see if the cabling of either is bad. For the magsafe side of the adapter, be sure the magsafe plug fully seats into your Mac. Being a magnet, it is possible the adapter and the connecter on your Mac could attract small bits of metal, and prevent a proper connection. Therefore, check and clean out both.
The final option for the power supply is its indicator light, which will glow green when supplying power and not charging the battery, and will glow amber when charging the battery. If there are any other colors or behavior such as red lights or blinking lights, then that indicates a problem, even if it’s a minor issue. If you are experiencing blinking lights on the power supply, then try resetting the system management controller on your computer, which can be done by following the steps in Apple’s SMC reset guide. Additionally, for systems built before 2009, try calibrating the battery by letting it run completely out, followed by charging it fully again after a 3-5 hour wait. This will run it through its full power cycle and have the system properly detect its charge level.
If none of these approaches show any difference, the adapter problems still continue, then you can try replacing the battery, the adaptor, or having the system serviced.