Should you connect the power cord to your notebook and then plug the power cord into the socket, or should you plug in the socket and then the notebook?

Are there any recommendations from Apple?


Update: I have seen both recommendations. Most of the advice says to plug in the notebook first. Maybe it doesn't matter at all?

  • I personally charge from either the power adapter or from the 27" Thunderbolt display, both of which remains plugged in to a power outlet which remains on all the time. Whenever my MacBook Pro is running low on power, I simply plug in the MagSafe 2 connector. – Nimesh Neema Mar 26 at 13:14
up vote 27 down vote accepted

Apple recommends to plug the adapter into the wall before connecting it to the computer.

For more information, go through the Apple knowledge base article, Using and maintaining your Apple MagSafe Adapter.

Connecting the MagSafe Power Adapter to power

Make sure that the AC plug or AC power cord is fully inserted into the power adapter before plugging the adapter into a power outlet. And be sure to plug your adapter into the wall before connecting it to your computer.

  • 5
    I wonder if there is a reason they recommend this. I've done it both ways without issue. – Alexander O'Mara Mar 26 at 16:05
  • 6
    @AlexanderO'Mara If the MacBook is already plugged in, there's a load on the adapter that would cause an arc as you go to plug it in. Not really much of an issue, but it's probably off-putting to the uninitiated. The laptop-end of the charger doesn't arc because the charger doesn't provide max voltage (~20v) until a handshake process has finished between the charger and laptop – Alexander Mar 26 at 16:34
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    @MikroDel IDK, people love micromanaging silly stuff like this, rather than just getting on with their lives and using these devices for what they are... tools. – Alexander Mar 26 at 17:12
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    IMHO, it's not silly stuff. The goal here is to get the most out the battery by maximising its lifetime. Apple notebooks, especially the recent generations are priced at a premium and the battery replacement could be a hefty deal for most if not all people. During the last 5 years of my using a retina MacBook Pro, I have burned my pockets quite a few times by getting a battery replacement once and burst charging port replacement twice. I hope that explains the micromanagement and silly concerns. – Nimesh Neema Mar 26 at 17:17
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    All this talk about arcing, existing loads and whatnot has me wondering if people are sharing the electrical mains with heavy loads like Bridgeport Milling machines or inductive crucibles. What kind of power is everyone plugging into? I seem to be missing all the fun. – Allan Mar 26 at 20:02

Plugging in a heavy load to a circuit causes arcing as the circuit is completed. Historically, this could damage wall outlets, plugs, adapters, and whatever was connected on the far end of plug (e.g. a computer). This would only happen when the device was in an "already on" condition, as classic devices used physical switches to connect the power supply to the motherboard. The classical advice was to plug in to a wall first for devices that might arc.

Modern devices have soft-switches and lots of protective circuitry, which is why arcing practically never happens and device damage is a lot less frequent than it was historically. The only practical time you might want to plug in to the wall first is if you're in a place that is known for power surges, but then again, you probably wouldn't want to have your device plugged directly into a unfiltered current to begin with (use a surge protector). In most practical cases, it doesn't matter which end you plug in first, but do use common sense.

  • Fried a power book like this back in the day. – AllInOne Mar 26 at 23:10

As hinted at in some comments, the safe procedure when using any electric power converter is to get the converter itself powered up and stabilized first. A wall-charger has caps to filter the load, and these should be allowed to charge up and eliminate any possibility of power surge at the output (the device side).

A well-designed AC-DC converter will have builtin arc and surge suppression, but you never know what you've got in hand. Caution is recommended.

As an extreme example, take a 50-kW Generac. If it's starting cold after disuse, it may take a minute or two to stabilize both the AC frequency and the AC voltage output. If you crossover before starting it up, undesirable transients could damage devices which "dislike" overvoltage or 40 Hz vs. 60 Hz drive.

  • 2
    Where do you buy your power adapters and accessories; the 1980s? Also a 50Kw generator is not a step down transformer that's by design isolated from the mains. It is, in fact, an analog of the mains. This would be a good resource to reference regarding switching power supply design: electronicdesign.com/power/… – Allan Mar 26 at 19:28

We always want to keep good maintenance of our electric products, and to make it have a long life before retiring it. There is reason why Apple wants us to plug the power adapter first, as I believe they want to put the load on the circuit in the power adapter before the Mac. It also acts as a buffer zone. It is cheaper to replace the power adapter than the Mac motherboard. Here is a link that provides the understanding of the arc.

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