Powering the Arduino from Wall Socket

I have found an adapter that fits nicely into the Arduino's power adapter.

I plan to power off the Arduino from a wall socket.

Is the adapter below (which I plan to use) is safe enough?

Uploaded with ImageShack.us

I'd say yes. 12V is an OK number.. Plenty of amperage. I assume since it runs a linksys device it is regulated? Have you measured the output with a meter?

Yup linksys device. A wireless-B router in fact.

Been using it for 6-7 years, and no unwanted incidents. I have no multimeters or such, so there is no way for me to check, apart from the fact that the router is still functioning even after severe thunderstorms and blackouts.

Would there be any difference if I attached the Arduino to the wall plug with or without any external hardwares e.g. motor shield, sensor etc?

It's not so much whether you have additional things connected that matters. If you don't know that it's regulated, you don't know what exact voltage it's producing. For example: I have a wall wart rated for 4.5VDC @350mA. With no load, my meter reads "13.1V". If I were to be drawing the 350mA it should be right around the 4.5V.

The Arduino has it's own on-board regulator so it can take higher voltages, but I don't know how high. You would probably be OK using that. Like I said, it was designed to power a wireless router(more sophisticated than an arduino).

Here's arduino duemilanove's reference page: http://arduino.cc/en/Main/ArduinoBoardDuemilanove Input: 7V-12V recommended so yes.

If you're using a different variation of arduino, check its reference, chances are they're the same due to the voltage regulators they use have the same recommended input voltages. The mechanical dimension on the plug: 2.0-2.1mm diameter on the pin so 2.x is your inner diameter. ~5.5mm outer diameter. I have an arduino board that has a picky power jack. I thought my wall adapters were bad until I got more arduinos to compare with.