|It shouldn't matter who made the card - the ATI chipset is the same. These days, the drivers / software for the card's video chipset are the same - made by ATI. |
They may or may not require you connect them together . If you are asking about this for the Ga-p55-ud3r, read the mboard manual regarding that, or see the manual for the card, or the AMD web site in the ATI support.
You need at least a 600 watt power supply to support two 5750s on a system.
"450 Watt or greater power supply with one 75W 6-pin PCI Express® power connectors recommended (600 Watt and two 6-pin connectors for ATI CrossFireX™ technology in dual mode)"
If you're a gamer...
In most if not all cases, the max capacity rating of the PS is an intermittent rating. It's recommended that you do not load your PS to any more that 80% of that rating if you are going to be using something that puts a constant load on it, such as playing a recent game for hours on end. In that case, you multiply the min capacity stated for the system with the particular video chipset on the card by 1.25 to find the min. capacity of the PS you should get.
600 x 1.25 = a minimum 750 watts.