Does anyone actually understand psu's

[Gegenki]

I'm so totally and utterly baffled.
I'm just about ready to switch out my psu after knowingly having a faulty setup for a long time which supposedly is living my graphics card with a lack of power.
My current PSU is rated at 500W with 16A on +12V1 and 15A on +12V2
I currently running
AMD X2 5000+
ATI Radeon X1950 pro
2GB of DDR2, 1 dvd drive, 1 floppy drive, 1 hard drive, 1 scsi hard drive with controller board, an addin network card (which isnt actually beinged used) and an additional 2 port usb bracket.

I'm considering upgrading to an ATI HD 3870. My current graphics card recommends 15A for a single card setup (and 30A for crossfire). I was told my PSU couldnt possibly handle that due to efficiency levels. Th 3870 recommends 26A on the +12V for a single card setup but I really don't understand how the amp rails break down when there are multiple rails and thus how expensive a psu I really need to go for.

[Viper]

Your PSU will do fine with the 3870. You combine the rail volts to get your total.

Does your PSU have a 75w 6 pin PCIe power connector? If so, you're good to go.

[=NukeBlaze=]

The power spec standard, ATX12V 2.0, recommends that all power supplies in modern system be made with two, or more, 12v rails to provide power to system components. This was done since more components draw power from the 12v lines, compared to relaying more heavily on the 3.3V and 5V rails of yesterday. Some companies make supplies with single 12v rails with 32, or high amp outputs. It all depends on the design they have chosen to use, and it if meets their performance/price goals.

Post the brand and model of the power supply, if you are worried. All power supplies are not made equal, regardless of what the wattage rating says.

[Gegenki]

It does have a 75W 6 pin pci-e connector
The PSU is an FSP BlueStorm AX500-A
Apparently its actual output is only 440W Maximum

I looked more closely at the label. For some strange reason in all these years ive had it ive been looking at the japanese section and never realised there was an english above it (reading upside down?)
17.5A on both 12V rails maximum
I assume the other 16A and 15A is sustained ampers.
The max wattage given for the 3.3V and 5.5V is 150W, Whilst the max for the whole system is 440W - so thats about 290W at peak (1.5 seconds per 30 seconds) for the two 12V rails

I ordered this this morning
http://www.awd-it.com/scripts/prodView.asp?idproduct=3442&product=Asus+ATI+Radeon+EAH3870%2DG%2DHTDI%2D512M+ HD+3870+512MB+GDDR4+DVI+HDMI+PCI+Express+2%2E0