Depends on your configuration , if you have a power hungry CPU like the AMD FX series , you can be pushing it with an r9 270x , considering you have a CPU of 150w TDP=
150w(gpu)+`180w(fx 8320 under full load) =330w already , throw in a couple of HDDs , fans and other stuff , and you will be pushing it for a 450w PSU , it also depends how much amperes you PSU can give on +12v rails , and also its efficiency.