How big of a power supply do you really need?

[gamerx456]

I'm building a cheap gaming rig for around $700, and I'm gonna be running a HIS Radeon HD 6850 and an AMD phenom x2 black edition 555 dual core that will unlock to 3-4 cores. What's the best way to determine how big of a power supply I need? Like I said I'm on a budget, and I'll downgrade the power supply wattage to downgrade the price
Is the amount of power needed by a power supply determined by the required wattage of the GFX card combined with the required wattage of the processor? Thanks

 

[obsidian86]

no more then 400 watts will be fine

 

[Ubrales]

To satisfy yourself, use these calculators:

http://educations.newegg.com/tool/psucalc/index.html
http://www.corsair.com/learn_n_explore/

To these calculated values, I would add about 20% for future expansion.

 

[Emperus]

How about this for 700$ -

Asrock 870 Extreme3
www.newegg.com/Product/Product.aspx?Item=N82E16813157198

AMD Phenom II X4 955
www.newegg.com/Product/Product.aspx?Item=N82E16819103808

2 x 2GB DDR 1333 MHz RAM
www.newegg.com/Product/Product.aspx?Item=N82E16820231275

Radeon HD 6850 1GB Video Card
www.m.newegg.com/Product/Product.aspx?Item=N82E16814150516

Samsung SpinPoint F3 1TB Hard Drive
www.newegg.com/Product/Product.aspx?Item=N82E16822152185

Asus DVD Writer
www.newegg.com/Product/Product.aspx?Item=N82E16827135204

Antec 300 Illusion
www.newegg.com/Product/Product.aspx?Item=N82E16811129066

Antec 750W PSU
www.newegg.com/Product/Product.aspx?Item=N82E16817371025

 

[Emperus]

How about this for 700$ -

Asrock 870 Extreme3
www.newegg.com/Product/Product.aspx?Item=N82E16813157198

AMD Phenom II X4 955
www.newegg.com/Product/Product.aspx?Item=N82E16819103808

2 x 2GB DDR 1333 MHz RAM
www.newegg.com/Product/Product.aspx?Item=N82E16820231275

Radeon HD 6850 1GB Video Card
www.m.newegg.com/Product/Product.aspx?Item=N82E16814150516

Samsung SpinPoint F3 1TB Hard Drive
www.newegg.com/Product/Product.aspx?Item=N82E16822152185

Asus DVD Writer
www.newegg.com/Product/Product.aspx?Item=N82E16827135204

Antec 300 Illusion
www.newegg.com/Product/Product.aspx?Item=N82E16811129066

Antec 750W PSU
www.newegg.com/Product/Product.aspx?Item=N82E16817371025

 

[jockey]

I'd recommend getting a 600W PSU simply because of your plans to unlock the 555. It will automatically want more power, and I feel that playing it safe with a higher wattage PSU would be a benefit for you. Plus the upgrade factor down the road.

 

[Altima NEO]

This helped me out when trying to figure out how much juice I needed.

http://extreme.outervision.com/psucalculatorlite.jsp

 

[gamerx456]

Best answer selected by gamerx456.

 

[gamerx456]

1. plenty of people buy phenom II x2 to unlock and plenty of them come crying to this forum when they don't.
2. benchmark reviews will often state how hungry a spec system with that video card will be during a stress test (non real world test) or gaming (real world). if your PSU can cover the stress test with a little head room then you are fine. luckily the AMD 6850 is very power efficient. see below. like obsidian stated a 400w PSU with most of its power on the 12v rail is plenty of power.
CPU: Intel Core i7-920 @ 3.33GHz
Motherboard: Asus Rampage II Extreme
Chipset Drivers: Intel 9.1.1.1015 (Intel)
Hard Disk: OCZ Summit (120GB)
Memory: Patriot Viper DDR3-1333 3 x 2GB (7-7-7-20
http://images.anandtech.com/graphs/graph3987/33245.png
http://images.anandtech.com/graphs/graph3987/33246.png

3. the amount of power needed is determined by all the hardware in the PC that require power.
4. make sure you purchase a quality PSU and not just the cheapest 400-500w you see. currently the antec earthwatt models are on sale and the 500w unit has plenty of power for your build and future upgrades. its a fantastic deal @ $55
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371035&cm_re=antec_500-_-17-371-035-_-Product

budget option at $35
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371033&cm_re=antec_380w-_-17-371-033-_-Product

That benchmark testing really helped