|The 9 volt power supply pushing 600 ma is probably straining to provide the power the router needs and quite possibly is a reason for your weak signals. You won't know for sure until you get the right one.|
A circuit will pull the amperage it needs and amp ratings should be considered a maximum the power unit is able to provide. For example your router may need 800 ma under full load but the manufacturer is going to spec something higher just to make sure. So you could use a higher amp-rated power supply since the router will only take what it needs.
That's different than the rated voltage. Voltage will be forced on the unit and while there may be some over-voltage protection and some built in tolerance for slightly lower or higher voltages you really don't want to vary the voltage much from what the manufacturer says it needs.
So if the manufacturer recommends a 12 volt, 1 amp input you could use a 12 volt, 2 amp power supply with no problem but don't use a 15 volt one.
Oh, and if you're randomly plugging in various power supplies you need to make sure the polarity (+/- orientation) is correct.
message edited by DAVEINCAPS