Replacing the power supply can't affect your connectivity in any way. It only provide power at the correct voltages to the computer.
Make sure that your new modem is correctly connected to the computer and correctly configured.
Particularly important if it connect directly into your computer and not through a router.
Double check your internet settings.
Check your firewall settings.
Unblock any application that you know should be able to access the internet.
Electro
May 2011