Quality.. Misc

I’d like to know the top 3 brand name available to Australia for Processor.. DDRAM.. Motherboard.. Sound Card.. Video Card.. Modem.. Power Supply.. CD/RW Drive.
What would be the best power supply to suit an AMD Athlon 1.8 Ghz, and what type of cooling fan?
What is the difference in more a 300 to 500 watt power supply.. why go for more power?