mister g said:
The title basically sums up what I want to know. I looked up how many Amps the PSU can support on the 12v rail and the PSU had two rails each carrying 18A. I don't know how many amps the Powercolor Radeon 5750 would require but I think it might work. Any other opinions?
What is the maximum output on the combined 12v rails. The 18A is considered peak amps not constant amps. Since each can peak at 18a, theoretically that means the 12v rails can provide up to 432w of peak power. However, both rails cannot peak at the same time so actual peak power will be lower. Peak power means for a split second or two.
The safest bet is to install a HD 5670 512MB since it uses very little power (under 30w).
The HD 5750 may be doable, but it depends on the rest of your system. I do not recommend the GTS 450 since it uses too much power for a 300w PSU. Seasonic manufactures high quality PSUs, but push it too hard and it will fail. A failed PSU can potentially damage every single component in your system; very rare, but it does happen. More common is maybe one or two components will be damaged.