iMac odd power ON behavior

Hi Folks,

I run an Apple OS X El Capitan iMac (20-inch, Mid 2007) 2.4 GHz Intel Core 2 Duo.

Unfortunately here in Guam we have frequent brown/black outs.

I have noticed that my iMAC automatically turns ON after a power outage which I prefer not to do. I ensure that in the energy/power settings options that I have unchecked "start up automatically after a power failure".

I do not use an uninterruptible power supply (UPS).

I have researched the forums and online and I have not been able to find a solution to my issue.

Care to point me in the right direction?

Thanks!