Graphics versus Power Supply


Jun 22, 2012

This website is a fantastic resource - this was my go to spot 15 years ago when I built my k5-90 machine so I could play duke nukem with my college mates. good times.

I've been away from PC gaming since 2003 and I'm looking to re-enter the market, primarily to play the new Mechwarrior which they say requires a quad core CPU and 8800GT or equivalent graphics card. After reading wikipedia for a couple days (boy was that fun...) I'm more confident than ever that I am totally lost.

So here's my strategy : get into this game as cheaply as possible. So I'm looking at used Core 2 Quad systems on eBay for $200-$250. The more I read, the more it seems like my problem will be power supply as I plan to add my own GPU.

So what wattage of PSU do I need in order to get 600-1000 GFLOPS of graphics performance?

It looks like I will have to be careful which graphics card I choose as the Radeon 6970 appears to max out at 250 watts but the 7750 maxes out at 55 watts?

Let's assume the CPU needs 95 watts (to the best of my knowledge that's the highest watt rating of the Core 2 Quads).

Can someone guide me here? Do you see what I'm trying to get at?


Nov 1, 2011
z68 mobo - 99.99
I3 - 2310 - 179.99
HIS 6870 - 169.99
2x4gb ram - 40.99
gigabyte case - 19.99
seasonic psu 520W - 59.99

570.94 - before shipping and OS... add a monitor keyboard mouse et voila

$250 old crust + $110 7750 + $60 reputable brand PSU = $420

I would definitely swing the extra 150.... plus that can be pared down a bit and still be sweet

replace cpu with i3 2120 -50 drop to 6850 another -30 4gb ram another -20
Sizing a psu can be very simple, or... complex and not very accurate. PSU calculators ask you for inputs about which you will have no knowledge. Eg. What capacitor ageing factor? How much reserve?

I have two simpler methods:
1) Look at the manufacturer recommendations. For example, AMD suggests a 400w psu for the 7750:

2) Look at how many 6 or 8 pin pci-e power connectors the card/s use. A 6 pin connector can deliver 75w, and a 8 pin connector can deliver 150w. Add that to the basic requirements of a pc which is on the order of 200-300w and you can get a good estimate of your needs.

It is not wrong to overprovision the psu a bit. It will run cooler and quieter under load. A stronger psu will only draw the wattage it needs, regardless of it's maximum rating.

3) A PSU is the last place to economize. A cheap psu will underperform, and if it fails, it can also damage anything it is connected to. Stick with known quality PSU brands. My short list would include Seasonic, Corsair, PC P&C, XFX, and Antec.

Know your seller on E-Bay. Check feedback carefully. Check the return and shipping policies. Pay with Paypal.

You can get a good deal. That is where I sell my old parts.
If the offer is for a complete pc, it often is a good deal; just check out the value of the parts. Most of the time, a seller will get more for the individual parts than for the complete pc.



Jun 22, 2012
I'm not building - I've been down that road before, I simply don't have the time or patience anymore.

Further refining my own thoughts. Amongst the pool of garbage on eBay, the only sku that works from a power supply POV is the HP XW4600 which is currently selling used for $150-$200 and then it has the PSU to power the 7750.

Done. :)

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