Can i use 12v 20A power supply to power Arduino Uno

I have an auto watering system but the 9v battery im using dies till the morning, so i want to use 12v 20A power supply to power it. Can i use 12v 20A power supply to power Arduino Uno? And will it burn?

If your watering system requires 12V then use it. If it requires less then use a lower voltage supply. 20A looks a bit oversized in comparison to the 9V battery you used before. Please give more information about the watering system components.

Why not? It is within the specs for Uno

Why should this matter?

Within the specs of the Uno, yes, but only if the Uno is not powering any other parts of the circuit with its 5V output. But if it is doing that, then the Uno's regulator can easily overheat and shut down or be damaged with 12V input. So we really need to know what the rest of the circuit looks like before we can say for sure that this is safe.

It works fine with 9V already according to OP, what makes you think that powering it with 12V will cause any problems if in fact it can take in up to 20V

Now my system looks like this: RTC and relay that connected to arduino and pump that uses 1 li-ion battery(pump is small). And arduino is connected to 9 volt battery. By the morning all LEDs on modules and arduino is off.

Post your circuit diagram plz

PaulRB already answered that. The onboard regulator has to drop the 12V (or as you say, theoretically 20V) to 5V, and as it's a linear regulator the current on both sides is the same. So the power to be dissipated as heat is 12-5 (or 20-5) x the current: the bigger the voltage to be dropped, the lower the current has to be to stay within the realms of reasonable heat dissipation. So it depends on what else may be driven by the Arduino 5V, which could add up to significant current.

I changed it so that RTC and relay i powered by another li-ion battery, and i will watch if problem will return.
p.s. I will send diagram of both

that’s assuming OP is already driving it on the edge, so 3V increase could cause a nuclear explosion

It's not an assumption at all: it's simply being prudent to point out a constraint that might otherwise be overlooked. It's common to think purely in terms of voltage for a regulator, perhaps forgetting the power aspect due to the delta-V x current.

No, i know that uno can handle 12v the question is about 20amps of power supply

Power supplies do not push- components draw what they need. If that wasn't the case, you would not be able to connect your house to your national supply up in the GW power range.

The concern raised earlier about the 20A being overkill was perhaps more to do with cost and physical size of such a unit, when a less capable one would suffice.

20A is how much current your power supply can pump through the load should the load require it. the only difference between low current and high current in you case is how much more spectacular your components will burn if you short circuit them or how much louder they will bang

how it was when problem occured(i forgot 9v battery)

how it looks now

So your 9v battery dies overnight with this configuration?

Thank you, because this supply is the only way to power from socket

no, with the first one