Would I be alright with this power supply?

I have a Dell 530s and want to upgrade the gpu to be able to play any game I want(not on high settings, but low-medium is fine with me.) Anyway it being a slim model is a pain in upgrading stuff so I have two choices of cards. A 9500gt(low profile) or a 9600gt(low profile). Anyway I also realized that my power supply is well under the limit of 400W for these cards at 250W. So I decided I should search for a new power supply but ended up finding out that my power supply is a TFX, and the highest I could find is 300w I've heard that the companies are usually really conservative on what the minimum power supply should be and also heard that some people actually got a 9500gt to work without flaws on a slim desktop at 250w. (as long as they don't have too many usb devices working.) I've decided to go with a 9500gt because I know for sure a 9600gt would use way to much power. I have some questions on what I should do though.

Here is my PSU model specs. http://www.atxpowersupplies.com/25 [...] 250D5W.php

I have 2gb of DDR2 333mhz ram and a Pentium Dual Core E2140 clocked at 1600mhz. My Motherboard is a dell 0RY007.

Graphics cards I'm looking into
http://www.newegg.com/Product/Prod [...] %20profile
http://www.newegg.com/Product/Prod [...] 6814187060

Would either my 250w power supply or a 300w that I upgrade to work with little to know flaws or damages with either of these cards?

If so which power supply, which card, and should I upgrade if both?

Is there a substitute I could use instead of a TFX power supply?

If none of these cards will work what card would you recommend that will?

Edit:
After looking at other gpus I might get a http://www.newegg.com/Product/Prod [...] 6814102799 Radeon HD 4550 instead. It seems to perform less than the 9500gt, but it looks like it will run any game. I want to make certain of that though. It only requires 300w as well. Should I get this?

Thanks I will get a 9500gt then. Is there a way I could measure how many watts are being used when I get it? I just want to see just to be on the safe side.

I was talking about while having the computer running using it to see how high my watts are going and if I'm cutting it close. Thanks though that is useful