Is my PSU adequate?

Hello to everyone :)

 Wasn't sure if this was the right thread, but still hoping to get some answers.

I am hoping to upgrade my little brother's PC as a Christmas present, yet I am still very new to PC building. 

At the moment there's a 450W PSU feeding power to i5 3470, a stick of 4gb 1600Mhz RAM (don't really know how relevant is this), some 7200RPM 500Gb hdd and just simple stock CPU fan.

Since there's a desire for better gaming experiance and integrated Intel Graphics solution doesn't cut it anymore I was thinking of buying a decent value-orianted graphics card. For intance, a overclockable gtx 650 or 7770..

So, my question is as follows - is the updrage safe with the old 450W PSU?

Thank you so much in advance :)



P.S. Have two more questions, yet, don't want to span the forum with multiple threads. Should I get additional fan or two for cooling if I get the GPU? And can I mix RAM stick's brands as long as the speeds and capacity matches? 

get the 7770, better performace over the 650. Your PSU should be able to handle the load. I would get some more case fans to cool the system temps a few degrees, and it is not recommended to mix ram. go with the same brand and model you have