GPU upgrade

[krenar41]

I'm getting an Acer Veriton S670G.
I'm not sure about the true specs(could 4GB ram,cpu the same):
Intel E8300
2GB DDR2
320GB HDD
Intel gma4500m(Not so great)
300 Watt 80% eficcient PSU(The main problem)
My question is does anyone know how much amps on 12v rails are.I can't find it.Can I upgrade to a 5670 or any good GPU without power connectors.
Please help me because I can't afford to buy a GPU+PSU or just GPU and fry my PC.

 

[krenar41]

Or can Someone tell me how much amps on 12v would be enough for a 5670.I have done a calculation :
Processor: 65 Watts
Memory: 1stick 2GB DDR2 (5 watts maybe,i don't know)
Motherboard:25 Watts
HDD:20 Watts
GPU radeon 5670: 60 Watts
The total consumption 175 Watts so 12V 16/18amps should be enough or am i wrong?

 

[C0rehound]

Here's a thread that should have some decent info for ya on a similar topic.