If you have two power connectors on that card you should really pick up a unit with two connectors as well...
This unit has two, and its really not that bad price wise.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817194090
The lowest 6770 on Newegg right now is about 100. Are you really willing to throw 100 dollars away, because you wanted to save 20$ on a power supply? You can always just watch the specials until one comes along for less. Newegg routinely has items go on sale for about 20 to 30 in your required watt range with the appropriate connectors.