Power supply ratings are their maximum output they are capable of. 
Computer power supplies are going to be oversized (if the computer was 
built right) otherwise they wouldn't last for very long and would run 
very hot.  Computers, especially modern ones,  power usage is going to 
vary wildly from one second to the next based on it's load and what's 
connected to it.  If your system is just sitting there, on, doing 
nothing, it will likely be under 100watts, especially if the monitor is 
off, asleep or non-existent.  Servers will tend to draw more, because 
they have a lot more fans, hard drives, and power profiles that don't 
allow for them throttle as much.

Even if you do have a system that only uses 50 watts normally, I still 
recommend getting something low power like a raspberry pi to serve your  
house because even if you have to buy the PI and the existing computer 
is free, the PI will quickly pay for itself and after that it's almost 
free to run it... and a lot more quiet and you also don't have to pay 
for your air conditioner to cool off the room that your higher power 
computer heated up which is also a very real cost that hasn't really 
been mentioned yet.

I had to argue with an electrician about power supply sizes when I build 
a computer lab with custom built computers with massively oversized 
power supplies.  He went around adding out all the wattage ratings of 
the power supplies and decided that my 30 computer lab would require a 
minimum of 15 circuits in order to not pop breakers.  I never could 
convince him that I was right, and that the breakers wouldn't pop and he 
finally did want I asked him to do which was to add 4 circuits, which we 
never has any problems with.

Brian Cluff

On 7/23/21 10:22 AM, Keith Smith via PLUG-discuss wrote:
>
> Based on what we have been discussing I assume my 400 watt power 
> supply may be drawing much less power based on actual usage. Therefore 
> maybe my computer might only be using 60 watts... making the cost lower.
>
> Your thoughts.
>
>
>
> On 2021-07-22 21:39, Mike Bushroe via PLUG-discuss wrote:
>> I usually use a mental rule of thumb that for every watt of 24/7/365
>> power consumption costs about $1 per year. Obviously this is failing
>> as electric rates keep going up. So to first order of magnitude a 100
>> watt server would cost around $100 a year, but if the server was using
>> the whole 400 watts it would cost more like $400 a year.
>>
>>>> If my home web server is using 100 watts an hour that mean 100
>> watts *>> 30 days * 24 hours or 72K watts.
>>>>
>>>> I'm thinking 72 * .1085 = $7.81 a month.
>>
>>                KINDNESS
>>
>> is most VALUABLE when it is GIVEN AWAY for
>>
>>                    FREE
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