My Arris Cable modem takes 115vac right into it and has its own DC power supply built into it. My Netgear WNDR3400 Cablevision Router has an external 115 VAC Plug in unit which puts out 12VDC and plugs into the Netgear router.
The important thing is to match the Power type (AC or DC) and the polarity of the plug matching the receptacle on the modem as to plus and minus pins. Of course this has been said several times here already, methinks
I am definitely not a pro plumber, but I am a pro crastinator
As an aside, one of the reasons for so many devices running on "wall wart" cubes..... anything running on 120 VAC has to be listed by UL or ETL or CSA. That listing process requires design considerations and many thousands of $$$$$$$$$$ for the application and cert. process. So you make 60 gazillion warts, which you get listed. The 12 volt device they feed does not require listing.
Follow up: I noticed that my DSL modem, 12 volts, IS UL listed. That may be because it is also connected to the phone line. Or, I may not have the whole story straight! I am blaming the chemo~!
Last edited by jimbo; 01-18-2013 at 08:27 AM.