Will my psu work with hd 4850?

The answer to your question is yes. However, the Antec Basiq power supplies are older models. As the model name implies they are basic, average power supplies similar to OEM psu's.

Antec offer some better quality units. Two examples would be the Antec Earthwatts and the Antec TruePower New series which are major improvements over Antec’s older psu’s like the Basiq models.

If you can manage it I recommend bumping it up a bit to an Antec Earthwatts or a TruePower New model.

 
jsc - I should not have said the psu old since it is only three years old.

Technical reviews at Xbit Labs and Hardocp of the Basiq 500U were not as good as Hardware Secrets. In addition there were some interesting comments in the Jonny Guru forum.

The unit does not have multiple +12 volt rails as advertised. The current on the +12 volt rail is low when compared to a high quality 500 watt power supply.

User comments seem to indicate a higher than normal rate of doa's and early deaths. Almost everyone agrees the psu fan is very noisy.