Posted 03 May 2013 - 10:33
The price alone of that box full of crr... err, PSU is a dead giveaway that you probably should not attempt it regardless of ratings.
Now to the rails. It's a distribution system. Each rail has its own overcurrent protection circuitry, which basically means this - if a short-circuit happens, only the stuff connected to that rail will end up in smoke, the rest will usually live.
Basically, if the manufacturer doesn't specify (as in this case), it's a guesswork. But in this case it's also easy - it doesn't provide the necessary cables. First, that is a clear indicator that the manufacturer is not confident at all about using it in any kind of multiple card configuration (therefore it's vastly overrated). Second - most likely processor, ATX and peripherals are on the first rail and both PCIE are on the second rail. If it hasn't crashed yet, I'm likely right. And there's not enough power left on any of the two rails to handle another graphics card of 6970 levels.
I might add, though, that one 6970 does *not* ever eat 370W. First, it'd be well outside PCI-Sig High Power ratings. Second, it's TDP is 250W, which means it would burn where it stands in seconds, if such power input would be sustained. You are likely confusing it with total system wattage. Actual numbers are about 210W, with 240W peaks.
Depending on the processor (if it's a low rated one, say 70W) and if you have just one HDD and nothing else, you *may try* with Molexes and hope that it holds and doesn't crash. But I wouldn't recommend at all.
I'd strongly suggest investing in a reputable PSU. And if you think about two graphics cards like 6970, then >50 amps on single rail configuration (starting from 700W) or >35 amps on *all* of the rails of multiple configuration is the minimum (also starting from 700W, not at all coincidentially, but very much in contraty to this overrated MS-Tech garbage can).