I am recently dismayed to learn that my 400W PSU (16A on the +12V rail) isn't powerful enough for a GTS 250 or a Radeon HD 5770, so I have no choice but to pick either a 9800 GT or a Radeon HD 5670. However, due to the scarcity of info on the vendors' websites, I am not even sure of the power requirements of these two cards.
(1) Although I read on GigaByte's website that 400W is enough for 9800 GT, I don't know if 16A on +12V is enough.
(2) ATi's website says that 400W is enough for Radeon HD 5670, but again I don't know if 16A on +12V is enough.
i would expect a 400w psu to have at least 20-25a on the 12v rail. It sounds like a very cheap crappy psu. you should upgrade it. get an antec earthwatts 380w. it has 2x 17a 12v rails and will be able to support up to a 6850 or gtx460.
Something like this is what you should look for.Although I have a feeling it will be drasticly more expensive in your country.But if it is the same price then I would put the extra money towards a better GPU.$20 more and you can get a 5770.
I've been using ASUS Radeon HD 5670 for a long time on a 450w Tech-com PSU which delivers a meagre 10 amps on the 12V rail. I've played games on full 1080p resolution with max possible settings and never had an issue. So I think you can go ahead with Radeon 5670 since it doesn't need external power source.
Although I am a bit curious about how much is the difference in power and amps requirement between a Radeon 5670 and 5750?