According to AMD a good quality 450 watt power supply is sufficient for an overclocked pc equipped with a single Radeon HD 5750 graphics card: http://www.johnnylucky.org/graphic-cards/gpu-power-requirements.html
Both AMD and nVIdia are conservative with their recommendations. Both companies overestimate total pc power requirements because there is a tendency among consumers to purchase very cheap, low quality psu's of questionable performance and reliability.
I am not familiar with the Dany 450W. I checked Google. The Dany450W appears to be a local or regional brand. There were search results for vendors in Karachi.
Normally I recommend Seasonic, Corsair, XFX, and sometimes Antec. However, they are not available in all countries. Which psu's are available in your country?