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I have a circuit that uses 2 DC supplies. I want one of the supplies to turn on at a later time in simulation than the first supply. How can this be done?

Is there also a way to simulate a supply turning on and off during the simulation so I can see how fast capacitors discharge?

Timed switches should work.

Assuming that you expect the output of the power supply to go high impedance when it is off then using switches is the simplest way to do it.

You can use the basic Time Controlled switch.

For more complex timings you could use an array of them switching at different times.

A more elegant solution might be to use the Voltage Controlled Switch and drive it from a PWS() source:

https://www.circuitlab.com/docs/expressions/

https://www.circuitlab.com/forums/modeling-and-simulation/topic/6h49s9xf/how-to-simulate-a-momentary-switche-being-pressed-every-few/

https://www.circuitlab.com/circuit/hsss64/pwl-type-source-can-be-used-as-part-of-expression-01/

Don't forget though that voltage (but not battery) sources in CL have zero output resistance so you will throw an error if you connect them in parallel without some finite positive resistance between them.

The switches in CL have a default ON resistance of zero.

:)