Thread: Upgrading, having trouble deciding on PSU

I am having a little trouble with the current crop of PSU calculators on the web giving accurate readings. Mainly on sites it gives me twice what others quote so hoping someone can shed some light on the subject.

My current setup - 500w Antec Smartpower modular PSU
Processor - Athlon X2 2.7ghz 7750 Kuma
CPU cooler -Rosewill RCX-Z940-SL 92mm 2 Ball CPU Cooler
Mobo - Gigabyte GA-MA770-UD3
GPU - SAPPHIRE 100265L Radeon HD 4830 512MB
RAM - Kingston HyperX 8GB (4 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066
Optical Drive - ASUS 22X DVD Burner with LightScribe SATA DRW-22B1LT
HDD#1 -Western Digital Caviar Blue WD3200AAJS 320GB 7200 RPM SATA
HDD#2 -Western Digital RE3 WD5002ABYS-01B1B0 500GB 7200 RPM SATA
HDD#3 -Western Digital Caviar RE WD2500YD 250GB 7200 RPM
Antec 300 w/ 2 LED 120mm intake fans, 1 120mm exhaust fan, 1 140mm exhaust fan
Vista ultimate 64bit

now the plan is at some point to drop a Phenom II 940 and Sapphire Vapor-X 4870 in using all the same equipment and PSU however when I look up a PSU calculator the majority of them give me a required wattage of 350w-400w give or take, NewEgg's version says closer to 700w, 700w seems extremely high to me as a 650w is the recommended amount for 2 4870's in crossfire. Can anyone point me in the direction of the right answer, or even a closer to correct answer then i am getting now? All the time and effort spent helping me on this is much appreciated,

Thank

An Antec 500 w Smartpower PSU has 36 amps on the 12 volt rails. That is about right for a good 500 watt PSU.

Figure 10 amps for the video board, figure 8 amps for an OC'd CPU, 5 amps for all the drives, and a couple of amps for fans and motherboard. You have enough power.

5 amps @ 5 volts for motherboard and drive logic, and 12 amps @ 3.3 volts for memory. My SWAG (Scientific Wild Assed Guess) is 360 watts. And I'm certain I overestimated a little in a couple of places.

I estimate that the PSU is running around 70% of capacity.

The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the 12 volt rail(s) can easily handle a system with any single video card made. A high quality 700 to 750 watt power supply can handle a system with two graphic graphics cards operating in dual mode.