The requirements say at least 400 watts but I used "extreme power supply calculator" and the results say that it uses less power than the GT 240. So I'm sort of confused and I'm wondering if the card will run on a 300 watt PSU. Thanks in advance for your replies!
the reality is, any generic 300w from HP, DELL, Acer or 3rd party brand name will run the ATI 5670 with an over clocked i7 CPU the total system won't break 250w
I very much disagree. There is no way anyone should ever run an overclocked i7 even without a gpu with less the 500w. thats just insane. Its not just the amount of power that is being drawn but how smooth the caps provide it and how it can handle its peaks. There isn't a 250w-400w psu out there that I would ever trust to run an i7 at anything over stock clock. Protect your investment, when in doubt go with something that is high quality and at least 100w over capacity. Good in case you add a bit more and when a high quality psu goes it rarely will take your whole system with it, a cheap one or one that is stressed to its max can and will much more often. oh yes don't forget you will tank your capacitors very quickly if your running max or if your power draw spikes go over rated wattage and instead of it lasting 5 years it will last 5 months.
i wasn't really trying to be a #### so sorry that i hurt your ego but as an electrician I know exactly what will happen if you run that system on a 400 w psu for any length of time. Also something that you are not considering are added strain from outside voltage fluctuations. Anything to do with electricity must be considered with tolerances. Just like the fact that every overclock requires a different voltage and will draw a different amount of power. That goes for everything in your entire system. On top of that you have to consider that incoming voltage while rated at 115 volts changes +/- 10% but i have seen it move even further as low as 94v from the wall. When you have fluctuations like that it has the same power effects on your power supply and can lead to system crashes and errors. Even a small change like increasing the clock to 4.0 on the i7 on the system you provided can add 20-30 watts of draw and consider extras such as dvd player and a few extra hard drives or extra case fans and you quickly get into danger territory. I am just saying what i would recommend and feel good doing so knowing that it wont be something that the person that i recommended it too will regret. Please calm down and understand that people in this world will disagree with you sometimes and it doesn't require you to attack them.
The problem of tolerances may very well be an issue with a cheap PSU; that's why no one around here recommends them. A quality PSU like an Antec, Seasonic, or Corsair tends to be over-built, and capable of outputting notably more than its rating, at realistic temperatures (e.g. 40c).