To make a long lived machine, you want to get the PSU rating to about 50% (1/2) of the maximum power draw. PSUs age and lose capacity so to avoid issues you select the PSU at what sounds like overkill at the time.
There are other common causes such as lack of routine maintenance such as canned air on vents and heatsinks and at about 3 to 5 years you need to replace heatsink compound. These are trivial low cost (well under 10 buck) items so it remains a mystery why this work is often not done before the owner reloads the OS, does driver hunts or falls prey to registry and computer system cleaners.
But all this is moot as we can't tell what machine we are chatting about.
Occasionally, when I'm on my computer my computer will randomly reboot. I've also noticed that sometimes like this morning when I'm not using my computer I can hear the fan start spinning almost like it just rebooted except not as loud. This will go for 2-3 seconds then it will stop just as suddenly as it started. Could this be due to a power supply trying to fail? Is there anything else that might be cause symptoms such as these?