PSU problem, amps maybe?

I'm a noob, building my first computer.

I have this system, and 2 power supplies. The setup works with one and not the other, Why? When the I say it doesn't work, I mean I switch it on, everything spins for 3-5 seconds then it shuts off.
CPU: AMD Phenom II x4 940 3.0ghz
Mobo: Biostar TA790GX XE
Ram: 4 gb (2gbx2) OCZ DDR2 800
HD: Seagate 7200.11 320gb
LG dvd burner
2 case fans, not sure what size, but not big, maybe 4"?


PSU A that works is an Antec earthwatts 430W ATX 12V v2.2
PSU B that doesn't is some no name 500W ATX
PSU B supports more amps on every voltage except 12v; it supports 14amps. PSU A has 12v1 17amps and 12v2 16amps.
So, my question is why would PSU B not run the system?

It is simple! The Antec is a quality unit with enough amps on the +12 volt to run your system, the no name does not have enough amps on the +12 volt to run a modern system.
Modern systems need amps on the +12 volt rail!
A quality 430watts is better than no name 500watt!

CPU, GPU and storage to start with. There are several psu calculators out there here is one http://extreme.outervision.com/psucalculatorlite.jsp
With a decent to good single dedicated GPU on a modern system the total amps on the +12 volt rail needs to be between 25 and 35 amps today based on the GPU.

From your description it appears as if the the no name psu has a single +12 volt rail rated at 14 amps while the Antec Earthwatts 430 has two +12 volt rails rated at 17 amps and 16 amps. I know the Earthwatts 500 has two 12 volt rails rated at 17 amps each.

I'b betting you also have a video card that requires decent amount of wattage and amperage.

I'm somewhat surprised that the no name doesn't work then. However, definitely keep using the Antec for now - it is the far better PSU of the two.

Corsair CX400 would be a good choice. If you want to put in a good video card at some point, you might want to go with something a bit better, perhaps a Corsair 550. As a general rule, Corsair, PC Power and Cooling, and Seasonic are among the best choices. Antec is often quite good as well.