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I have a 2020 MBP 16", and I bought two Dell P2721Q, which are capable of delivering up to 65W through the USB-C port. Could connecting 2 of these simultaneously somehow damage the computer?

I want to use these 2 monitors as external displays. I know that macs can drive 2 4K monitors without problems, I'm simply concerned about the power delivery through multiple ports in the MBP.

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  • What about power delivery has you worried? The Mac doesn’t power displays as they get mains power.
    – bmike ♦
    Feb 8, 2021 at 15:12
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    My concern was on whether connecting multiple devices that send power to the MBP could somehow damage it. I've seen that connecting multiple chargers to the MBP can indeed prevent it from charging again. My concern is along those lines.
    – Mateo Torres
    Feb 8, 2021 at 18:05
  • I have MacBook Pro M1 Max and 2 displays LG 27UL850-W connected via USB-C. Mac's power adapter was connected as well. After some days USB module in one of the external displays was damaged when I opened Mac's lid. After that I checked HDMI input — it was working. This is why I'm interesting in this question too. Was it a random hardware accident or power delivery issue? In any case I still have warranty and the display is in the service center now.
    – C0DEF52
    Dec 28, 2021 at 10:12

3 Answers 3

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Connecting two power supplies to a MacBook Pro will not damage it. The computer will simply choose to take power from the device providing the most power and if they are equal then the first one plugged in. If both monitors are on and the MacBook Pro powered off then on power up the computer will likely simply choose a monitor to take power at random.

Unfortunately a MacBook Pro is not capable of taking power from two supplies at the same time, so plugging in two 50 watt power supplies will not net you 100 watts of power but only 50 watts. If your monitors supply only 65 watts, and you need 87 watts to avoid draining the battery due to high CPU load, then you should plug in an 87 watt power supply in addition to the monitors. This is assuming you have more than two USB-C ports on your computer.

Apple planned for this in their design so don't be concerned about shorting anything out by plugging in more than one power supply to you MacBook.

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  • Thanks you very much!
    – Mateo Torres
    Feb 8, 2021 at 1:41
  • I've started a second post asking for details. It's entirely possible for things not to work as apple described...
    – NJL
    Feb 8, 2021 at 1:55
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I am not sure why you think there would be a power problem. The Apple specifications state up to 4 displays with 4096‑by‑2304 resolution at 60Hz and the Dell P2721Q specifications state a native resolution of 3840 x 2160 at 60 Hz. The monitors includes a hub, so I would assume the 65W through the USB-C port comes from the monitor, not the Mac. In other words, the monitor has a powered hub.

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  • I understand that the monitor is the one providing power to the mac. But my question is whether it's safe to plug two monitors (both of which provide power). Another way to put it is whether the mac can handle multiple 65W coming from multiple ports.
    – Mateo Torres
    Feb 7, 2021 at 23:47
  • Evidently, the Mac communicates with the monitor before the monitor delivers power to the Mac. I would assume the Mac would not request both monitors to deliver power to the Mac.
    – David Anderson
    Feb 8, 2021 at 0:48
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Yes, any device can damage another when there are cables and signals and physical attachments, but that would be an exceptionally rare event.

As long as all hardware is functioning, there’s no benefit or harm to connecting things to see how it works, though. Daisy chaining displays is on the way out with Thunderbolt 3 and USB 4 since the hubs are becoming quite inexpensive.

I would connect things straight and make sure everything is working first before you try chaining.

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  • Thanks, could you elaborate please on how should I go about connecting 2 of such monitors to a MBP?
    – Mateo Torres
    Feb 7, 2021 at 21:42
  • I'd want to check with Dell but I think these might be monitors that you can daisy-chain. EG plug one into the Mac and the other monitor into the first one. I've personally not done this but I think that is the meaning of upstream and downstream ports.
    – Steve Chambers
    Feb 7, 2021 at 21:57
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    Downvoted this answer because it is too general and lacks connection to the specifics of the question. This could be the answer to just about any question about connecting anything to anything. OP was not asking a metaphysical question about the nature of technology.
    – jay613
    Feb 8, 2021 at 1:39
  • Thanks @jay613 I answered the first version of the question and it too was basic. Looks like others have covered this well now. I’ve updated this to reflect what the question is asking now. Again, appreciate all the votes and comments. I don’t take up or down votes personally and appreciate the sharing of perspectives.
    – bmike ♦
    Feb 8, 2021 at 3:34
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    Well done @jay613 and I feel bad I didn’t thank you for being an active reviewer and a good one at that. This site is lucky to have people like you helping.
    – bmike ♦
    Feb 9, 2021 at 0:23

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