Excuse me, I need a power supply for my devices, but don't know how to choices to appropriate with these devices. Can you help me? How to calculate
to find voltage and ampere of a power supply for these devices?

My device number 1: 12V and 0.25A, device number 2: 12V and 4.5A, device number 3: 12V and 4.5A.

 

hi seil
Welcome to AAC
The basic PSU would be 12V at 10 Amps.
What are the three different devices being powered.?
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Thank you for your respond. These devices are one of cooling fan and two of Thermoelectric Peltier chip. Excuse me, can you tell me how to calculate it for the result?

 

hi,
To calculate the result, as all the Voltages are 12 Volts, just add the Amps together 4.5A + 4.5A + 0.25A = 9.25Amps.

The nearest standard power supply would be 12V at 10Amps.

 

This is where location helps a little. One can interpret your question as 3 different supplies or one for all of them.

Your output is 12 V. Some supplies are unregulated. Some switchmode and some linear (heavy, low noise, wastes power)

The current just needs to be greater than the sum (0.25+2*4.5)=9.25 Amps; So you need >10 A; 10 A would be a common value.

Stuff with motors is tricky, but a small fan should not be a problem.

 

Thank you everybody for your knowledge, but I have additional questions as well if one or two of these devices has been removed, how does this affect other devices?

 

It will have no effect, the connected devices will only draw the current/Amps from the power supply, they need to operate.

 

Can overflow ampere for the device and then damage?

 

No, a device will only use the current it needs to work.
Think about your house lights at home, you can plug in a 40Watt or a 100Watt lamp, both will only use the current they need to work.

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Now I understood and I will remember this knowledge. Thank you so much!