Studio Display fails to connect when powering MacBook Pro

Subject: Studio Display fails to connect when MacBook Pro is powered by the display

I am reporting a potentially reproducible Studio Display connection issue that may involve power delivery and/or Thunderbolt initialization.

Hardware/software configuration

• Mac: MacBook Pro with Apple M3 chip
• macOS: 15.7.5
• Display: Apple Studio Display
• Display type: Retina LCD
• Resolution: 5120 × 2880 Retina
• Studio Display firmware: Version 17.0 (Build 21A329)

Problem

The Studio Display was powered on and connected to the MacBook Pro, but the MacBook Pro would not establish a display connection.

At the time of the failure, the MacBook Pro was being powered by the Studio Display through the Thunderbolt/USB-C connection. The MacBook Pro was not connected to its own power adapter.

Workaround that resolved the problem

I connected the MacBook Pro to its own Apple power supply. I then disconnected and reconnected the Studio Display to the MacBook Pro.

The Studio Display immediately connected and operated normally.

No other change was made to the MacBook Pro or Studio Display.

Significance

This suggests that the Studio Display may not always successfully establish the display/Thunderbolt connection when it is simultaneously supplying power to the MacBook Pro.

Connecting the MacBook Pro to its own power supply appears to change the power-delivery state sufficiently to allow the Studio Display connection to initialize successfully.

This may involve USB-C/Thunderbolt power negotiation, power-delivery prioritization, Thunderbolt initialization, Studio Display firmware, macOS display detection, or an interaction between these systems.

Recommended troubleshooting step

I recommend that Apple investigate this behavior and consider adding the following troubleshooting step to Studio Display support documentation:

If your Studio Display does not connect to your MacBook, connect the MacBook to its own power adapter, then disconnect and reconnect the Studio Display.

This is a simple troubleshooting procedure that could potentially resolve the problem without requiring the user to replace cables, reset hardware, reinstall software, or seek service.

Because the Studio Display is designed to provide power to a connected MacBook, a user would reasonably expect the MacBook to operate normally without its own power adapter. Consequently, a failure caused by—or associated with—the Studio Display's power-delivery state would be difficult for a user to diagnose without specific documentation.

I believe this behavior warrants investigation and documentation by Apple.