Is this going to work?

[Sorriow]

short story, I have 2 computers. I used to play with my old one, until the motherboard and CPU were damaged. It's no longer in use tho.
My current computer has a great CPU, but has serveral hardware issues (crappy GFX, 300w power supply...). You can see the stats below.

In my old computer are still 2x ATI Radeon HD 4800 Series. I thought to exchange the nvidia 520 GS in my current PC with one of these. Since I'm low on money, I can't afford a now one. Will this work?
Also, do you think I should get a 500w (or even higher) power supply when I do this? I don't think 300w are enough for the Radeon card...

OS: Windows 7 Home Edition (64 bit)
Motherboard: Cleveland
Processor: i7-2600 CPU
Memory 8gb DDR3-1333
GFX: Nvidia Geforce GT 520
Hard drive: SATA 1,5TB
Power Supply: 300w

[Mormolyce]

AFAIK those two cards are both PCI-E x16 so there's no reason you can't put the Radeon in your current PC. Obviously you cant put the Geforce back into the old computer alongside the other Radeon, but if I'm reading you right you aren't using the old one anyway.

Newegg has a PSU calculator to tell you the wattage you need (there's lots on the net but Newegg's seems to be pretty up to date):

http://educations.newegg.com/tool/psucalc/index.html

If your old PC's PSU is still intact couldn't you swap that across as well?

[counterhero]

Ok, first off. you have a 300 dollars cpu and you are cutting corners on your video card and power supply? I don't get it. But anyways. Why can't you take the power supply out of your old computer that were running those video cards and put it in your new one with one of the cards. Maybe both if your mobo supports crossfire not just sli.

[Sorriow]

Ok, first off. you have a 300 dollars cpu and you are cutting corners on your video card and power supply? I don't get it. But anyways. Why can't you take the power supply out of your old computer that were running those video cards and put it in your new one with one of the cards. Maybe both if your mobo supports crossfire not just sli.

A friend of mine sold this PC to me for about 500 bucks, because he no longer needs. My old one crashed in november, so I didn't have a Computer for a while. It's not a selfmade computer. It's one of these shitty models from the computer market.

The PSU of my old one lack of quality. I already tried to build it in my current system, but it seems it has been damaged aswell (energy gaps, pretty noisy). It don't want to screw up my current computer too.
Besides that, this motherboard doesn't support crossfire afaik.

So, do you think 500w is allright? Or should I consider buying a 750/800w PSU?

EDIT: Haven't seen the link for the calculator. I check it out. thank you