yes on my radeon all in wonder 9800 pro box it says:
"ALL-IN-WONDER 9800 pro requires connection to your PC's internal power supply for operation. A 300-watt power supply or greater is recommended to ensure normal system operation where a number of other internal devices are installed"
so pretty much 250w will power it but you wont get normal function if you have a bunch of other upgrades in your computer...I would go with at least the 300watt power supply since thats what im using now.