Problem with Sparkle 560

I just got a sparkle 560 (non TI).

I have an old Korean 550 watts PSU with 18A and 17A on two 12 volts rails. Usually system runs well and I can also game on it too. But using graphics software like Poser and Cinema 4d my system begins freezing for a second intervals, but no big shut downs.

Also my system is core I5 24000, DH67CL, 10GB kingston RAm (4+4+2).

I want to know is there is a PSU or driver issue as I didn't had a clean install. I un installed my old card drivers and installed the new drivers and card need two 6pin connectors, while PSU has only one and I'm using molex to 6pin for the other slot.

Also I was planning to buy the Xigmatec 500/600 watts PSU as it has two years warranty but all good PSU are currently out of stock at the place where I'm living.