What size psu do I need?

[Maxwh2o]

I want to have crossfire xfx 6870's(only one for now), and a i5 2500k overclocked. Will a 750w corsair tx750 work for that?

 

[hunter315]

Yup, it will be plenty for that setup even with overclocking. Guru3d saw a pair of 6870s only pulling around 430 W from the wall so you have plenty left for OCing
http://www.guru3d.com/article/radeon-hd-6850-6870-crossfirex-review/4

 

[Maxwh2o]

On newegg it says sli-yes but crossfire-no how does that work they both use the same power.

 

[hunter315]

The SLI-certified/ready and Crossfire-certified/ready are equally meaningless. A vendor can send in their PSU to either AMD or nVidia who look at it, call it pretty, slap a sticker on it and send it back. Look through the list of SLI-certified and crossfire-certified PSUs, most of them should never run more than a pair of 6450's in crossfire.

Take this unit for example
http://www.newegg.com/Product/Product.aspx?Item=N82E16817338008
SLI ready and crossfire ready, probably wouldn't survive it's first experience with either. With 20A on it's 12 V rail, my 955 and 4850 would push it over it's limit, let alone crossfire or sli.