Everything works well, but now I have to change the Video Card and get a GTX 550 Ti. My problem is that I've seen in different sites the power consumption of the GTX 550 Ti, and it varies from 116w to 400w, so I don't really know if it will work on my generic PSU. It's not that I don't want to buy a new PSU, it's just that there is no "Thermaltake", "CoolerMaster", etc. in my country, just random brands that are not listed as good PSUs. For example, a guy offered me a "RAMBO" PSU (I know, it must be generic) of 1000W for U$100. The only TWO non-generic PSUs cost around U$300 (800w) and U$400 (1200w), which is extremely out of my price range.
So. I want to know if I can run this system with an ASUS GTX 550 Ti instead of the XFX GT 520, considering that my PSU is a generic Delux ATX-750W P4 with 51A.
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That's horrible luck that you can't really get any better PSU, but the one you have should work. Even the worst 750W units should give you around 500W I would imagine, which is still more than enough for that system. I'd say you should be fine.
Thank you, now I can buy the video card without any doubts. This PSU shall suffice until I get the money to buy a good PSU.