Right...the new Atom is here! Where's the on/off switch? What's all this? DC in?? Nobody said I needed an external power supply as well....
If you've gone through the above thought process recently, this page may be of help to you. It will probably also save you about �50 on E-Bay.
Let's get the general principles out of the way first.
In its normal configuration, the Acorn Atom needs an 8 volt DC power supply. In this configuration, the Atom has two voltage regulators soldered onto the motherboard at positions IC53 and IC54.
There is an alternative. Some Atoms (like mine) do not have the two voltage regulators but instead have links 6 and 7 on the circuit board made. In this arrangement, the Atom needs a 5V regulated supply.
Anyhow, with any luck your Atom should have the two voltage regulators in place so you can proceed to getting it an 8V DC power input.
The next thing to consider is the current the Atom requires. This depends on how upgraded it is. The very basic 2K Atom draws about 800 milliamps from the power supply. By the time you have added all the extra RAM and 6522 VIA it needs 1600 milliamps, or 1.6 amps. With the expansion bus in use, the Atom can require up to 3000 milliamps, ie. 3 amps.
The original Atom power supply is an 8V 1600 milliamp DC supply.
To power your Atom without the proper transformer, you will need to nip down to the shops and buy yourself a power adapter. They usually have a switchable voltage and multiple ends for different connections. Make sure it goes up to at least 9 volts. You may get away with 7 volts.
Make sure it has the right current. DON'T buy a cheap one for �4.99 as this will only be a little thing supplying 300 milliamps which won't be any use at all. The type you need is a digital camera power adapter. Make sure the packaging says something like "2500mA" in big writing on the front.
You probably won't be able to check the connectors that come with the power supply unless you can open it in the shop. You are not really likely to carry your Atom down to the shops with you so you will just have to take pot luck. If you have an Acorn Econet type 2 clock, you could take this with you as the power connector is the same as in the Atom. DON'T USE the Econet clock transformer as it is 12 volts and WON'T WORK and will probably bust the Atom as well.
You might have to buy more than one power supply to get the right connector and the right amount of current. This is what I had to do, although I already had them at home. The right connector was in a 300mA unit which goes up to 12v. I used this on my digital camera 2500mA adapter to work my Atom, although it only goes up to 7 volts, but it seems to do the trick.