Power Supplys and System performance

I have a customers machine doing funny things, not a stranger to us. Power supply is 300w and devices connected pretty much max it out while at idle. Will the start-up draw of a cd/dvd recorder or another device cause other parts of the motherboard to get flaky? If I install 400W I have laying around, could it make the start-up problem go away? I’m pretty sure it only happens when the customer pushes the system to the max.