DC Adapter and 5-volt Regulator
Here we have a common AC/DC adapter (transformer), that gives you various voltage outputs and connector types. You can get a cheap one at a discount shop, for $/€ 3 or so, which is fine for many things, but it's nice to have one that gives more power in case you want to run small motors and so on. The cheap ones are rated around 300mA of current; the one shown here gives 1000mA but might cost $/€ 15 or so. Recently there is a new kind on the market called a "switching" power supply. It looks very similar, but gives a higher current rating (1000-2000 mA, or 1-2 A) in a smaller and much lighter package. The switching supplies (usually) work with both 110 and 220 volts, great if you travel.
The picture on the right shows one way to connect power to the solderless breadboard. These parts should perhaps be in the "common ingredients" page, but I install them on my breadboards fairly permanently, so I think of them as "equipment". Many digital logic circuits run on exactly five volts, which is not provided by the DC adaptor. So here you see:
1. the connector jack to plug the DC adaptor into. Bring your adaptor to the store, so you can check that the plug fits! There are several different sizes.
2. a filter capacitor, about 1000 mF or so, rated at least 16 volts.
3. a "7805" five-volt regulator.
4. an L.E.D. light to show the power is on.
5. a 220 ohm resistor for the L.E.D.
You can also use a power supply from a computer. It’s already regulated to 5 volts, so you don’t need the regulator circuit above. It gives you five and twelve volts, and a LOT of current! For example, while the above adaptors might give 300-1000mA, this will give you up to 20,000mA (20A). Great for running larger motors and giant robots. Sometimes these don't seem to work when not connected to the motherboard of the computer, and will require a light bulb or large resistor on the 5v supply. The ones I've found in Europe seem to have less of a problem with this. On the other hand, many of them have a switch for 110/220 volt operation, which is great if you want to take your work across the ocean without worrying about electricity supplies.
Note that the ground (black wire) is often connected to the AC mains ground. That means, for example, that you can’t put two 12-volt supplies together to get 24 volts, the way you can with a transformer.