Installing graphic card with limited Power Supply (275W)

yes
it may cause damaging yor system and vga card

I have done a 6570 with a 250 watt slim dell before so I think 6450 in your pc is fine since 6450 uses less power than a 6570.

Just one note though, 6450 is a horrible graphics card in terms of performance. It has less performance than the HD 4000 for instance which is an integrated card...so depending on the processor, you might not even see any benefits with a 6450.

That's what I'm worrying about a bit.
And since I have a small form factor Dell, suitable power supplies are hard to come by.

I've google around and the seasonic ss 300ftx 300W seems to be the only choice I have.

Which in the end is fine I guess, a new power supply plus a low end video card would cost me around 120 dollars.

Thanks.

Thanks for answering.
I've read multiple people saying they didn't had any problems after installing a video card even though they're power supply wasn't sufficient.

So I'm still doubting whether to upgrade my PSU or to just go ahead and install the card anyway.
It's a pretty old compter, I belive from 2008 so I'll have to buy a new one in the near future. So I dont wanna spend too much on the old thing.

And no, I'm not playing any video games or editing videos or anything. I just browse the internet, edit some text and I check out some Yotube videos. Nothing really that needs a powerful graphic card. But anything is better than NO video card at all, I'm now dealing with onboard graphics so I'd won't mind upgrading.