Yes, you can run it in SLI. As long as the sub-catergory coincides (57x ... HD 6850 and 6870....6950 ad 6970), then the two cards can be SLI'ed.
Your power supply has enough wattage but make sure it is a reputable brand you can rely on. If the PSU is poorly manufactured, it an break when stressed under load and possibly, explode in your case.