What to look for when looking for PSU for my 2x 7870 XTs?

[King Mustard]

I have done the Power Supply Calculator and it shows around 650W, so I'm sure 750W will be enough.

Apart from 750W+, what else should I be looking for?

I keep hearing about rails or something

 

[Liquid_Static]

The most important things to keep in mind with PSU's is reliability, having enough juice for your system, and efficiency, in that order.

1. DO NOT buy a generic PSU, you will regret it and you may fry your components, stick with a well known brand that uses well reputed OEMs (e.g. Corsair, Enermax, Antec, Seasonic, Silverstone NZXT, or even Rosewill).

2. Having enough juice for your system is important. Having too much is unnecessary and will actually make your PC less efficient. I'd say a 750W unit for your system is a fine choice, although you could likely get away with 700W. DO NOT go purchase a 1000W power supply because the number is bigger. A while back, some PSU manufacturers used to get larger wattage ratings by building units with multiple 12v rails. This is not so much of an issue anymore, and practically any unit you buy nowadays uses 1 rail for stability and convenience.

3. Efficiency of the unit should be taken into account. Simply put, do not buy anything less than 80+ Bronze for a high performance build. Your electricity bill will thank you.

While there are other considerations (modular vs. nonmodular, noise etc.) those are the main things to worry about!

 

[lehtv]

Rail setup - not relevant. What matters is quality. If the unit is well designed, it will run just as reliably with multiple rails as with a single rail, assuming equivalent maximum output from the rail(s). A good example is Antec's Delta-built Platinum units versus Seasonic's Platinum units - they are pretty much equals, despite entirely different rail setups.

Quality is best discerned by reading a professional review of the particular unit, as units from the same manufacturer always differ a little, or in some cases a lot. Don't be fooled into thinking a particular PSU brand is always going to put out the same quality units, as they can target different markets with different units, and use different OEM's for the actual manufacturing.

Brands I'd typically recommend: anything from Antec, Corsair, Seasonic, XFX. Super Flower Golden Green or Platinum. Some LEPA, Enermax, Silverstone, Cooler Master, Rosewill units. That's about it.