Planning to upgrade - Help needed regarding PSU

Hello,senior members.....I'm planning to upgrade my old PC, for playing the latest games. I have two graphics cards in my view - AMD R9 270x 2GB DDR 5 or Nvidia GTX 960. Both of these need at least 600wt as far as I know, so I'm going to buy Corsair 650Wt PSU for that. Presently I have APC Back-UPS 600. If I go with either of these cards and the Corsair 650Wt PSU, do I have to go for a new UPS too?? I'm worried as we have frequent voltage fluctuation in our area..... and also I don't have AC in my room, so I have to depend upon CPU coolers only. And also,how much the electricity bill will be affected with this 650Wt PSU???

jits said:

And also,how much the electricity bill will be affected with this 650Wt PSU???

The 650W psu doesn't actually use 650W all the time - it's the maximum it can supply (although in practice psu's are 80-90% efficient). The psu delivers however much the pc draws, up to its max rating. So swapping out a 650W psu with a 800W psu will not use any more electricity at the mains socket. The pc uses more electicity when say encoding a video (high cpu) or hard gaming (high gfx).

When calculating psu watts, it's a good idea to go for a slightly larger capacity than the bare min required, to give yourself a bit of extra headroom. However - don't go crazy and get a psu that's way larger than you need, because a (say) 1500W psu running at 30% of its rated capacity is less efficient than a 650W psu running at 75% of its max. In that scenario, on the same pc, the larger psu would use a bit more electricity.

Thank you all for your answers...
@IanDrexP - Yes I'll certainly go for a 650Wt PSU,Corsair, if the budget allows me.
@RoasterMen, I've used the utility and edited my system info...some places are blank still, I hope to get my new system in the next week,and then fill up the new specs.
@badcrc,I'm definitely not going to buy anything larger than a 650Wt PSU...I think my budget allows me to go as far as 650Wt only.
Thank you all again for these prompt replies.....

Jits:

Before you buy ANY power supply, tell us what brands and models in the 500 to 650 watt range are available to you from your suppliers.

Or better yet, post a direct link to your suppliers so we can see what they have to offer.