side note: If you don't need all that RAM, your performance may also improve slightly without the motherboard fastmem installed. As you're doing video work, I guess you may use a lot of RAM though.
also, if you don't have a good surge protector already, I wouldn't even have the machine plugged in to a bad mains supply. It's too much to risk, when surge protectors cost such a small proportion of your total computer price. In the same way, I think a suitable UPS would also be a worthwhile investment.
If you want to replace the power supply, make sure you check the voltage and current specs for each voltage, not just the total power output. Power supply quality is really important in electronics performance and reliability.
