a psu like seasonic s12g 450 (450w, 80+ gold rated psu) will work. if the s12g 550 is cheaper, then that one would be better choice. an other option could be xfx 550 TS power supply.
the keywords about your current psu would be - peak and combined. "peak" does not mean "continuous" - which is the kind of current supply a pc requires. and "combined" often hides the fact that minor rails are rated for higher current delivery and the important +12v rails cannot sustain high loads.