When does a mac laptop startup automatically after a power failure?

I'm trying to get the hang of this. I notice that sometimes when I plug the charger the macbook boots automatically, other times it doesn't. I know in desktop macs this is determined by a setting in Energy preferences, but not sure when this is supposed to happen with macbooks. Does it change with the model? It's good to know this for troubleshooting. Any insights would be much appreciated.

Regardless of of the Mac model, the power settings determine if it will boot upon power failure. If this option isn't set, it won't boot.

It appears that this feature is controlled by a parameter in the Mac's NVRAM (non-volatile RAM, which contains various parameters used during the startup process). The parameter in question is AutoBoot, which controls whether the MacBook will automatically boot when the lid is opened or power is connected (note that there appears to be no way to separate these settings—if you disable boot-on-power, you also disable boot-on-lid-open). The %00 value for this parameter disables automatic boot, and %03 re-enables it. These values can be changed using the nvram command-line tool.

So, to disable automatic booting when power is connected, run the following command in the Terminal application (found in /Applications/Utilities/Terminal.app) by copy-pasting it into the Terminal, then pressing return. Note that this must be run by an administrator account.

sudo nvram AutoBoot=%00

You'll then see a prompt that looks like this:

Type your password, then press return. Nothing will appear on the screen as you are typing; this is normal.

To revert the changes (i.e., to restore the automatic booting behavior), execute the following command (once again as an administrator):

sudo nvram AutoBoot=%03

After entering your password (if prompted), the setting will be reset to the default.

To view the current values of the data in NVRAM, run the command nvram -p in Terminal. Look for the key on the right-hand side called AutoBoot. If this is set to %03, the laptop will automatically boot after a power failure (i.e., when re-connected to AC power); if AutoBoot set to %00, it won't.

Note that NVRAM values change from time to time, so this may not be applicable in the future. Moreover, if modification of these values causes further issues, you can reset your NVRAM to its factory state by following this process.

Here's an article with more information about the NVRAM parameters on the 2016 MacBook Pro.