Monitor power supply through Thunderbolt 4 on M4 Mac mini

Question

Level 1

4 points

Monitor power supply through Thunderbolt 4 on M4 Mac mini

Both monitor and Mac mini are mains powered so by connecting both by their TB4 slots what is happening to the power supply capability of the thunderbolts connection from the Mac mini as both devices are connected to the main electricity supply?

[Re-Titled by Moderator]

Original Title: If I connect a mains powered BenQ 27" 5k monitor to an M4 mac mini using Thunderbolt 4 ports on both devices is the monitor still drawing power from the thunderbolt cable?

Mac mini (M4)

Posted on Jun 30, 2025 09:32 PM

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Answer 1

Jul 1, 2025 10:59 PM in response to Kawshus

USB-C and Thunderbolt standards allow for negotiated Power Delivery, in either direction. Whether such Power Delivery takes place is up to the devices.

Mac notebooks will accept power from an AC-powered monitor or dock, but Mac desktops such as the Mac mini expect to get power from their own AC power supplies. Apple says that the M4 and M4 Pro Mac minis can draw maximum continuous power of 155W, leaving open the possibility that consumption might briefly be higher.

Desktop monitors like the 27" BenQ 5K monitor expect to get power from their own AC power supplies. The ones that have USB-C or Thunderbolt inputs frequently will offer to share some of their power with a computer – using USB-C Power Delivery. (According to the BenQ site, the BenQ 5K monitor has a normal power consumption of 40 watts, and a maximum power consumption of 230 watts. It can deliver up to 90 watts of power to a computer.)

Portable monitors may try to draw power from

Their own internal batteries, if they have them,
Their own external power supplies, or
A computer

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Answer 2

tbirdvet

Level 6

16,715 points

Jul 1, 2025 05:17 AM in response to Kawshus

The TB cables and the mains have nothing to do with each other. The TB cables are used for processing data/audio/video, etc. only not for powering the Mac or monitor.

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Answer 3

Kawshus Author

Level 1

4 points

Jul 1, 2025 07:11 AM in response to tbirdvet

But is seems they also can power charge “Thunderbolt 4 ports and cables support the trifecta of power charging and data transfer with bidirectional movement and video display in one interface. For example, with a Thunderbolt enabled laptop, display, and a cable, the laptop can pass a signal to the monitor and the monitor can charge the laptop at the same time. (Up to 100W of power for laptop and up to 15W for computer-powered accessories.” - Intel.com

The BenQ 5k monitor and Mac mini both have Thunderbolt 4 ports but if both devices are plugged into the mains what is happening to the power charging (up to 100W) aspect of the Thunderbolt 4 port/cable connection?

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Answer 4

Rudegar

Level 10

178,860 points

Jul 1, 2025 02:28 PM in response to Kawshus

people report that the mac mini m4 can get a bit hot, if it was possible to power a monitor using the psu inside a mac mini then I would not advice it, monitors may use around 100watt and with psu inside the mac overhead this could generate some heat.

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Answer 5

Kawshus Author

Level 1

4 points

Jul 2, 2025 12:12 AM in response to Servant of Cats

Thank you one and all for your helpful replies. My concern was putting too much power into a device if it was mains fed and receiving additional power through a TB4 connection. I now see this is not the case. Appreciate all the input (no pun intended)

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