I got two devices, the 1st device needs 12vdc and the 2nd device need 12vdc 1.5A.

Is it ok to use 1 power source that outputs 12vdc 1.5A for both devices?

 

1.5A plus (something) is greater than 1.5 A
so, no.

 

Does that mean different power source for each device? thanks a lot

 

It means that you can't get more than 1.5 amps from a 1.5 amp power supply.

 

How much current does the first device need?

 

Are you asking is it ok to run both devices at the same time from the one supply? If so, the answer is 'no'.

 

How much current does the other device need? Your power supply needs to be able to source current greater than the SUM of the current required by the. Two devices.
For example, say the first device requires 500mA. Then, the supply must be rated for greater than 2A. That is 1.5 A plus 0.5A (500mA).

 

No tech words, the current of power supply as the money in your pocket, the drawing current of device as the cost of stuffs that you want to buy, do you have the idea now?