If its this PSU, it has enough power for that system + 4850.

But never heard of the brand before.

wklzip

It does not look like that PSU.

I use the Audio Technica ANC7. They are good if you have a loud PC.

Reviews here: http://www.amazon.com/Audio-Technica-ATH-ANC7-QuietPoint-Noise-Cancelling-Headphones/dp/B000OMKR8E

He have an Okia 550w PSU, is this enough for an HD 4850?
Okia is a generic name brand?
What is the worst that can happen if he buy the card and hook it up to his PC?

He have a E7200, 2GB ram, 1 HDD, and 1 DVD drive and some case fans. Not a very power hungry PC at all.