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The iMac has its own power supply but I'm wondering what would happen if I would connect an additional power supply to my iMac (M1 2021). The reason for the question is, the Anker 675 active docking station uses only one cable for both data connection and power supply.

For laptops this is obviously very desirable. However, now with the iMac, where only the data connection is needed, what would happen if the docking station is connected? The docking station in question lists iMac as a compatible device but could this damage the iMac, or the docking station itself, because it is always connected and trying to power the iMac?

2 Answers 2

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The docking station in question lists iMac as a compatible device but could this damage the iMac, or the docking station itself, because it is always connected and trying to power the iMac?

Your iMac will ignore the charging capability of the dock.

Just because the capability exists, doesn’t mean it is implemented. Remember, with the USB-PD specification, charging power is negotiated and if nothing is negotiated, nothing is sent. It’s not sending raw power to the iMac, you can’t damage anything. (At most, there’s a 5V reference signal, but that’s within specification).

In short, it will just be a data connection and not a data and power connection.

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  • I think that a connected device providnig power is against spec. But not unheard of and usually gracefully handled by host. idk if this particular dock would deliver any power without being asked though. Commented Mar 22 at 15:45
  • @akostadinov, ...it was against the earlier / pre-USB-C spec, certainly. Commented Mar 22 at 19:48
  • @CharlesDuffy, so with USB3 it is allowed? Commented Mar 22 at 21:13
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    @akostadinov, ...I had to do a bit more research to fact-check myself -- the ability to change the power role independent of the data role is a power delivery extension, not part of base USB-C; that said, it is now standardized; see ti.com/lit/wp/slyy109b/slyy109b.pdf?ts=1711125530933. Commented Mar 22 at 22:04
  • Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Ask Different Meta, or in Ask Different Chat. Comments continuing discussion may be removed.
    – Monomeeth
    Commented Mar 22 at 22:41
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The iMac will not be damaged in any way, as long as USB-C is connected to a correctly implemented charger.

The charger tells the computer how much power it could supply (say 85 Watt), and the computer tell the charger how much charge it wants (in this case 0 Watt). And the cable tells both how much power it can handle, say 60 watt. So the charger will send 0 watt to the iMac. It would send 30 Watt to an iPhone that can handle no more than 30 Watt, a MacBook would get 60 watts because that’s what the cable can handle, and with a better cable it would be 85 Watt because that’s the chargers limit.

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  • Are you certain that an iMac can be powered via USB?
    – Allan
    Commented Mar 21 at 22:00
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    @Allan Huh? Why are you asking that? The answer does not say that an iMac can be powered by USB.
    – nobody
    Commented Mar 23 at 18:35
  • First sentence.
    – Allan
    Commented Mar 23 at 18:49
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    @Allan the first sentence doesnt read that the iMac can be charged by USB-C, just that it wont be damaged if connected to a charger following the specification - the iMac wont ask for power, and the charger wont supply it.
    – Moo
    Commented Mar 23 at 23:00
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    @Allan sure you can, if the iMac has USB-C. Literally just tried it with my iMac and my USB-C dock that I normally use for my Macbook Pro - connects fine, iMac has access to the peripherals, iMac doesnt draw a charge from it. Thats the same dock which charges my Macbook Pro.
    – Moo
    Commented Mar 24 at 0:18

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