The Asus EAH5450 is said by Asus to need a 400 Watt minimum poser supply, so in theory your 550 Watt unit ought to be OK, except that we don't know whether it is a 'no-name' cheapo PSU with an optimistic or just plain false wattage rating or a good solid quality PSU. The fact that you cannot find a maker's name kind of suggests the former. A lot of cheap PSUs get stressed when asked to deliver power near their maximum claimed rating. Of course the card might be faulty and need to be returned.