Sleep will NOT wake up

I recently acquired a Dell Optiplex 3050.  I've now completed setting up the preinstalled Windows 10.  I've owned and been using Windows computers for nearly 30 years now.  Sleep is something that's been around for a very long time and always been kind of innocuous.

However on this computer sleep is behaving quite strangely.  When the sleep mode is exercised, either intentionally by selecting Power>Sleep or automatically after preset time delay, if I try to awake it fairly soon after it went to sleep then operation is restored as expected.  However, after it has been in Sleep mode for a long time it seems to have gone into a deep sleep and nothing I do will awaken it.  Even briefly pressing the Power On/Off button will NOT awaken it as commonly occurs on laptop computers.  The only way to continue using the computer is hold the Power button long enough to perform shutdown/power off and then reboot the computer.

I have looked through the user guides to see if there is something special (i.e., different from all other computers I've used) that needs to be done to awaken it from such a deep sleep but have not been able to find any explanation.

Can someone please explain what I'm failing to recognize.