I know that you guys are probably mad at me, because this question appears everywhere on internet! But yust to be sure! I have max 300W psu and I have to buy a new graphic card. I have this in my mind:
ATI radeon 5450 1GB, but recomendations says taht I need at least 400W psu! I've heard alot about AMD overstating the power requirements of their lower-end cards. My old graphic card:
I would be safe and run with 500watts of power, you cant go wrong with that, whats your budget for a PSU I bet we can find you some nice ones to fit your budget.
(Radeons have tendenct to suckup more power than NVIDIA so a 500W should be fine)
The 5450 only draws like 20 watts max. I dont know what you have for a CPU but the most it could possibly draw is like 125 watts, throw in the board, drives and fans and stuff, and your at 150-175 max draw. Now add in the 5450 and your still below 200 watts.
I would not waist time on the PSU upgrade.
On a side note the 6450 only costs about $10 more uses only about 18 watts of power and is a good bit faster. I would grab one of those if you can.
You have no reason to upgrade your power supply for that card. It has no PCIe 6- or 8-pin connectors, thus it will be powered through the connector on your motherboard. 300 watts is more than enough to run the card with that system.