INSPIRON 546 POWER SUPPLY UPGRADE

Hi i just called Dell technical support, and i learned that the Inspiron 546 i want only has a 300 watt power supply. The technician on the phone said that it would be risky for them to put in their 500 watt power supply due to the motherboard getting fried. I am really disapointed about this because i was hoping to be able to use on of the following graphics cards ; gts250, gtx9800, radeon 4870, 5770, etc. Please if someone knows of a power supply upgrade that will work with this system would be hugely appreciated. Buying a more expensive computer isn't an option unfortunately at the moment.

HERE ARE THE SPECS!

COLOR- Piano Black edit
PROCESSOR- AMD Phenom™ II X4 820 (2.8GHz, 6MB) edit
OPERATING SYSTEM- Genuine Windows® 7 Home Premium, 64bit, English edit
PRODUCTIVITY SOFTWARE- Microsoft® Works 9 edit

MONITOR No Monitor edit
MEMORY- 4GB Dual Channel DDR2 SDRAM at 800MHz- 4 DIMMs edit
HARD DRIVE- 320GB Serial ATA Hard Drive (7200RPM) w/DataBurst Cache™ edit
GRAPHICS CARD- Integrated ATI Radeon HD3200 Graphics edit
OPTICAL DRIVE- 16X DVD+/-RW Drive edit
SOUND CARD- Integrated 5.1 Channel Audio edit
MEDIA CARD READER- No Floppy Drive or Media Card Reader Included edit


THANKS