|> You can download the ATX12V Power Supply Design Guide version 2.2 here:|
A 350 watt supply rated by one supplier is also rated as 500 watts by another. And nobody lied. They simply measured different things. Why those two numbers rate the same supply is obvious with necessary electrical knowledge, basic design experience (guess who has that), or an analysis using other spec numbers.
OP’s 12 volts is defective. Whereas these numbers are not identical to those in ATX12V specs, both numbers say same thing. Multimeter numbers are based in how voltages are measured, what is actually being measured, and how a multimeter works. When under maximum load, those power supply voltages must exceed 3.23, 4.87, and 11.7 volts. And yes, a multimeter can report numerous things from those simple measurements; when one learns how power supplies work or even designs them.
Review numbers provided by the OP. Another potential problem exists; seen only because he posted those numbers.. Apparently the computer has too much load on the 3.3 volts for that supply as compared to the 5 volts. Remember that myth about wattage? The meter shows why wattage says almost nothing useful. That supply could have more than enough watts. And most of those watts are lost on the 5 volt rail. Only current for each voltage is relevant. It appears that supply has more than enough power (watts) on 5 volts, barely enough on 3.3 volts, and is woefully undersized on 12 volts. Supply could have more than enough watts – just too many located on wrong voltages.
Another fact - if a power supply damages a motherboard or other components, the power supply was defective by design. Damage directly traceable to the human who bought or installed that supply. Since so many computer 'experts' have zero electrical knowledge, then an extremely profitable market exists dumping inferior supplies. Supplies that even violate industry standards such as UL and FCC. These same supplies will *forget* circuits that make motherboard damage impossible. Why can they dump these supplies in North America? Who are they selling to? A+ Certified computer techs who need not even know how electricity works to be certified.
A minimally acceptable supply starts at $60 retail. That does not say a $90 supply is better. But that does say a $30 supply is probably selling for an even higher profit margin by *forgetting* essential functions - such as the circuit that makes motherboard damage impossible.
Again, jam's numbers are correct. But then add other facts such as how a multimeter works and the various failure modes to convert those spec numbers into valid readings. By not learning this, jam would never understand why different multimeter numbers and spec numbers say the same thing. When under maximum load (that means the OS multitasking to every peripheral simultaneously and not disconnecting any wires), then those multimeter numbers must exceed 3.23, 4.87, and 11.7 on any one of each orange, red, purple, and yellow colored wire. Yes, three voltages - four wires.
"Volts times amps" assumes a perfectly resistive load. Computers are reactive loads. Total power required may not be the same power consumed. And so the difference between two numbers - watts and volt-amps. Add that to the specmanship game where a 350 watt supply can also be rated as 500 watts - when marketed to computer assemblers.
However, for a computer, all that is made easily irrelevant, instead, by viewing current for each supply voltage. Then by confirming those numbers are sufficient using a multimeter when the supply is under maximum system load - when the supply is powering everything in the computer simultaneously.
A defective power supply will still boot a computer. The OP's 12 volts was defective - and the computer still booted. Of course. Only way for a layman to identify a defective supply long before the system crashes is to use a multimeter. Only way for the OP to obtain useful replies from the more technically knowledgeable posters: numbers from that multimeter.