How to start old power supplies from PC

A switch mode power supplies for free !

The old power supplies can be used for a lots of diy project. This is the best way for having a good power supplies already stabilised, with switch mode, for free.

Difference behind switch mode power supplies & linear power supplies.

Switch mode power supplies : A switching power supply is a power supply whose regulation is provided by an electrotechnical component used in switching (generally a transistor) and using a high-frequency transformer.

Linear power supplies : A filtered rectified power supply is a power supply in which the electrotechnical component is used in linear mode (equipped with a diode bridge + a capacitor) and uses a conventional transformer.

So switch mode power supplies is used for will give a very precise current, while the other no. So for precision electronics, that's what we need.

If I want to power my arduino card in 5V, that and perfect.

J'ai sur mon alimentation des sortie 3v 5v et 12v.

You just need to find the two points on the board, which act as a switch. The connected ones. The power supply will then work as soon as the connection

I am quite specific about the terms used. I hear a lot of people talking wrongly about a transformer.

The transformer only operates on AC power. It lowers a voltage. For example 220V AC to 50VAC and AC only.

If you see the term transformer used in a continuous current project, then it is not a transformer but a converter.

Simply because the transformer can be used in a diagram for the realization of a converter.

I have AC power, I want DC power. So I use a transformer to lower my AC voltage, later I will use for example a diode bridge to be able to have the current in one direction.

Okay but if I want to then increase my output voltage which will be in continuous current, I use a transformer?

No it is not a transformer but a converter. I am talking about the converter step up here.