Why do I need a 300W PSU for AMD 1.2

[Ak]

Can some one explain to me why do I need a 300W PSU? I am running 3 different Duron O/Ced to 950 with 235 W. Wll my system crush? I have three very good PSU, SPI, Delta. Should I buy a new one while my system is working? I am planninf to put a 1.2 G CPU next week.

Thanks

AH