What is the safe voltage range for a 7.2 VDC / 200Ma power supply?

I have an ATT 2Wire DSL Gateway Modem Model 2701HG-B, with a bad power supply, I need to know what I can use in place of this one, everyone I have seen on the net complains about them not having sufficient voltage and amperage, and the power supplies burn out rather rapidly, I want to kick it up a notch so what would be a safe range, one that I won't fry the modem when I plug it in...