Capacitor at the output of mobile charger circuit

[Yasserbn]

I am using a wall cell phone charger which has (+5 volt output) to run my own circuit.
The circuit has a micro controller and three relays.

I know Engineers put capacitors at the output of the voltage source (+5). I think these are filters for banning high frequencies. How much should be the value of this capacitor? and what type of capacitor (ceramic, polarity)?

 

[alec_t]

I'd try 470μF, electrolytic, at least 12V rated; plus respective ceramic 100nF decoupling caps directly across the supply pins of the micro and any other IC.

 

[audioguru]

A "cell phone charger" is really just a 5V power supply. It has an output capacitor to filter out mains hum and other noise.
Your circuit should have its own filter capacitor at where the DC enters it. 0.1uF for a digital circuit or 47uF or 100uF for an audio circuit.

The cell phone has the charger circuit inside that is powered from the 5V power supply.