50c is perfectly fine, with that cpu you only need to worry if it goes over 60c. The stock cooler is fine as long as you are not overclocking or living somewhere very hot. An overheating cpu wouldn't smoke, the pc would shut down long before it got hot enough to do that. I haven't got the pc in front of me but knowing just how poor that PSU is and that smoke usually only ever comes from a failing PSU I am making an assumption that's what is happening here. I don't want you to use the pc anymore because if I'm right which I believe is very likely that PSU could fail completely at any time and potentially damage other parts of the pc.