A cheap psu is false economy.
What was wrong with your original psu?
A cheap psu will not deliver advertised power, it will deliver it not on the +12v rails where you need it, Will be rated at peak watts, not continuous, Will deliver only at room temperature.
It will have fewer circuit protections so if it fails, it can destroy anything it may be connected to.
Here is a decent list ranking psu's by quality tiers:http://www.eggxpert.com/forums/thread/323050.aspx
And... it matters exactly which 4800 card you have.
Here is a chart of what you may need:http://www.realhardtechx.com/index_archivos/Page362.htm