Mac turns off the power supply when it sleeps
The system is powering off because AutoPowerOff is enabled.
To disable it, issue the following command in Terminal:
sudo pmset -a autopoweroff 0
That command will set autopoweroff to "disabled" for all profiles (-a). This means it covers you when on battery and on A/C. If you just want autopoweroff disabled when on battery, use the following command:
sudo pmset -b autopoweroff 0
-
-b= battery -
-c= (wall) charger -
-u= UPS -
-a= all profiles
See man pmset for more details.