I going to buy a 1gb asus hd eah5670...I have a 450 watt zebronic psu..The main problem is that my psu has 20 amps on the +12 volt rail but it need atleast 26 amps...So can i run it....Without no problem..
Depending on the rest of your computer you probably do not need a new PSU. 20 amps on the 12v rail is 240W, but of course that's probably peak and not sustained. Even so, a 5670 is pretty miserly and will generally use well less than it's max 75W (6.25A on the 12V) so long as you're not running furmark . You should read this article on x-bit
You probably don't NEED a new PSU, like Megamanx00 said, but I would not trust my system to a "zebronic" PSU. I will only buy name brand PSU's as I've had the cheaper brand PSU's blow and take most of my build right along with it. Go with one of the ones that Shubham listed- all are good and reasonable prices, and will serve you better in the long run as well.