I've recently purchased a Gigabyte Z77-D3H Intel Z77 Motherboard, a Intel Core i5-3570K 3.40GHz processor and a XFX Pro 550W Core Edition to slap into my computer...I'm now in the market for a top notch graphics card and I've got my eye on a Sapphire HD 7970 VAPOR-X GHZ...Will the power supply will suffice? I had people advise me that it DEFINITELY would on the forums and I've just checked with the supplier I got all the kit from and they said that it wouldn't be enough!
What do all you lot think? I'm still within the return window for the psu so I might just send it back and get a bigger one before I start putting it all together.
A quality 550W PSU -- assuming you're getting at least +30A on the 12v rail -- is about right for a 7970 and plenty for a 7950.
7970s are 250W and 7950s are 200W max load. Add in 80W for your CPU, and an overly ambitious 100W for the rest of the system, that leaves you at 430W (7970) or 380W (7950) max power usage -- which you would never approach outside of stress testing. You'd even have a comfortable margin for overclocking.
For reference, I run crossfire 5850s (150W each) and an overclocked i5-2500k (95W) on a 600W PSU with no issue. People vastly overstate what's needed, but looking at the label and doing a little arithmetic is all you need to calculate it. Yes, you don't want to skimp on your PSU, but there's also no benefit to overspending.
edit: I just looked your PSU up. 44A on the 12V rail and 80+ bronze rating... you're completely fine for any single GPU setup.
just built a pc for a relative with a i7 3770k and a 7970 (not OC'd) using a seasonic 520 (80+ Pt) and did a test running MoH:WF. Just as long as your PSU is solid (and as previous posters said yours is very solid), 550W is plenty for your system.