I'm a person who has no idea how many watts is runnin my comp and how to tell.

No way of knowing that that I know of.

Well I think you can get an estimate by reading the manuals of the products.. they should tell you ~ rails and if you add them up that should give you a some-what knowledge.. I think? Right..?

if its a Dell or likewise it should be stated someware in the docs,otherwize pop the cover off and look for a tag on the PSU.

The manual and the PSU label will only tell you the Maximum power your computer could draw.
For a guesstimate of what it actually consumes tryTHIS

If you have a 400 watt PSU it draws 400 watts of AC , what the comp and related componits use are something else.
But if it is 400 watt the transformer and bridge rectifer are useing 400 watts even if nothing is hooked up to it , simple phyisics.
Anytime you convert AC to DC or vice virsa the input is a fixed value,what you consume on the other side is different , these values can be added up for a very close guestament.

Sorry Pappy, but the power rating on a PS is the total combined power that it can deliver on the DC side.

Example, our 300W PS's here can draw 7A at 115V which is 805W under full load...

and the 300W of output is divided up between all the dc voltages.

???? You sure about that pappy ????

http://www.jscustompcs.com/power_supply/

A 400-watt switching power supply will not necessarily use more power than a 250-watt supply. A larger supply may be needed if you use every available slot on the motherboard or every available drive bay in the personal computer case. It is not a good idea to have a 250-watt supply if you have 250 watts total in devices, since the supply should not be loaded to 100 percent of its capacity.

According to PC Power & Cooling, Inc., some power consumption values (in watts) for common items in a personal computer are:

Accelerated Graphics Port (AGP) card 20 to 30W
Peripheral Component Interconnect (PCI) card 5W
small computer system interface (SCSI) PCI card 20 to 25W
floppy disk drive 5W
network interface card 4W
50X CD-ROM drive 10 to 25W
RAM 10W per 128M
5200 RPM Intelligent Drive Electronics (IDE) hard disk drive 5 to 11W
7200 RPM IDE hard disk drive 5 to 15W
Motherboard (without CPU or RAM) 20 to 30W
550 MHz Pentium III 30W
733 MHz Pentium III 23.5W
300 MHz Celeron 18W
600 MHz Athlon 45W

I guess i missunderstood the question,I have in my hand here a 400 wat PSU,it states that it draws 100-127 volts and 10 amps when energized , regardless of its max output witch is 4oo watt DC total.
the dc side and ac side are two seperate circuits,so the supply side is going to be a constant , that is what i was getting at.
as far as power draw for the comp itself , look at ace's post.
One thing i do know is a healthy comp , like this one should be on its own ac circuit in the house.

There is actually two answers to this question depending on which watts you are interested in. If you are interested in total system watts to size a power supply then read Ace's reply and add up the load. Rember to add all the fans and auxilary stuff that is plugged in and select a supply that has at least 20% additional capacity.

If you are interested in how much juice the computer and monitor are contributing to the electric bill the monitor is easy read the back label. The computer is a little harder as the actual line load will vary depending on how much the power supply is powering. Because there is inherent loss in the power supply the line load will always be higher than the DC rating of the power supply. This extra energy is being disapated as heat generated in the power supply.

Lets say your computer is drawing a total of 7 amps at 120 volts (this would be a pretty serious home computer) that equals 840 watts input. If your computer is on 24/7 you will use 20,160 watts per day or slightly over 20 kilowatts. our electric rate here in NY is around 13.5 cents per kilowat hour so it will cost around $2.70 per day to run. Spread over a year that figures out to $985 dollars, lot of money to surf around