Could someone set me up with some 'general rules' around source impedance/resistance, and why it is important? I mean in relation to power supplies such as a battery. I understand that any device's output is going to have an associated impedance, even a power supply, but do not 'get' what sort of impedance say, a 9V battery or a transformer, is going to offer to the following circuit. So I don't know what to 'assume' the impedance of an AC source or a battery should be in circuit simulation, etc., and how it affects current flow to the device it's powering. It's easy to figure out what a transistor's output Z will be, but a power supply??

It's not like you can measure a battery to find its internal impedance

For AC, is the DC resistance of the secondary sufficient to assume its impedance? Or would one have to go thru the steps of finding L and C reactance and actually do the impedance calculation? Could be difficult if the L and C values aren't known...how's that done?

Thanks in advance for your input!

~Mike