Standby mode no power on

Entering standby Standby requirements are different for notebooks and desktops.
For a notebook to enter standby, it must be running on battery power and have no external connections (such as Ethernet, USB, Thunderbolt, SD card, displays, Bluetooth, and so on).
For a desktop to enter standby, it must have no external media mounted (SD cards, USB, or Thunderbolt storage devices).
Exiting standby To exit standby, do any one of the following:

• Press a key
• Click the trackpad or mouse
• Open the lid on a notebook
• Plug in a power adapter on a notebook
• Plug in a display

When the computer exits standby, the state of the system image stored on the flash storage is used to restore the system to its pre-standby state. The computer returns to full operation within a few seconds.
If you leave a notebook in standby long enough for the battery to deplete fully, the computer will shut down. You can recover your computer to its pre-standby state and any unsaved work should not be lost. To exit standby at this point, attach the computer to an AC power source and press the Power button.

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Mac computers About standby