Well, it seems that not all power supplies are equal. I had a shock yesterday (not literally that is) when I hooked up a power meter to my arduino-powered XBee-to-ethernet gateway controller. It measured a staggering 14watts !
Not this 14-watt monster that's for sure.
Curious, I measured other electronics gizmos I’ve built, and they were all taking 14 watts ! “That’s just wrong, way too high” I thought. My revo always-on dual-core-atom server only takes 35 watts. A tidly little aruino project should take next to nothing…
It just wasn’t making sense until I realized it was the power supply taking all the juice. Another power supply I had was showing 0.00 watts while powering the same geek-devices – it was just too small for my meter to measure. “Thats more like it” I thought.
I did the measuring with one of these:
Why do I care ? Well, I leave my arduino projects on all the time. 14watts = 14 pounds sterling per year = too much to bear.
Having said this, I use the switchable power supply to get different voltages, which is handy, as I don’t have a “lab bench power supply” like the pros in white coats do:
So now I’m out looking for a power supply in the UK…
Current front-running is this one from HobbyTronics: http://www.hobbytronics.co.uk/mains-psu-9v?keyword=power%20supply
However, it’s an un-regulated supply, and I read somewhere that “switched mode” supplies are more efficient.
So what should I be looking for ?
http://www.arduino.cc/playground/Learning/WhatAdapter had some useful advice: “9 to 12V DC, 250mA or more, 2.1mm plug, centre pin positive”.
It sickens me to see that http://www.allelectronics.com sell these in the USA for $3.50, but i can’t see anything similar here in the UK for 3 times that !
For example:
http://www.awatronic.co.uk/acdc12v500ma/prod_20714.html is ~£10 plus postage.
http://www.amazon.co.uk/gp/product/B003JFYXW4?ie=UTF8&tag=shopwiki-uk-21&linkCode=as2&camp=1634&creative=6738 is £1000 ! Ok. I guess that’s a joke, and I’m not surprised they still have stock.
Suggestions welcome. Still searching…
Update: Well, the power block from HobbyTronics HobbyTronics: http://www.hobbytronics.co.uk/mains-psu-9v?keyword=power%20supply works a treat. 300ma at 9v, reading 0.00 on my meter 😉
Loads better than 14 wattts any day.
Time to order a few…
Cobweb 
ModMyPi stock a 9V (http://www.modmypi.com/arduino/accessories/power-supplies/arduino-universal-power-supply-9v-2a) and a 12V (http://www.modmypi.com/arduino/accessories/power-supplies/arduino-universal-power-supply-12v-2a-high-voltage) Arduino power supply.