It might be that your new psu is bad as well.. I just had to replace the psu in my pc because it was causing all kinds of strange symptoms. It first started with two usb ports falling out randomly, while there was no issues with stability otherwise.. I really did not suspect the psu at all considering the system was stable otherwise even during heavy load.
A few weeks ago it turned itself of with a snap sound whenever i tried to enter bios or if i used the dvd burner/dvdrom which then lead me to believe it was the psu.
I replaced the psu yesterday and now everything works including the usb ports which has not worked for ages.
Watt does not always mean much anyways since there isnt much of a standard in the PSU world. A good 350watt might for example have more amps per volt line than for example a cheap 400watt psu.
