Can a linear power supply be used for multiple devices?

"So, if you have two 12V devices, and each needs 1 Amp, then your power supply needs to put out 12V at 2A or more."

This topic comes up often and I'm still a little confused. You seem to imply that you can feed more current than what's spec'd on the wall wart. So are you saying if a device has a 0.5A @ 12V (6 Watts) wall wart, you can supply it with 1A @ 12V (12 Watts) without issues?  Last time I tried this the device got too warm to touch. I thought the LPS needs to match both the V and the A (or mA) of the wall wart its replacing. 

So are you saying if a device has a 0.5A @ 12V (6 Watts) wall wart, you can supply it with 1A @ 12V (12 Watts) without issues?

In almost every case, yes. The one time I've seen an exception to this had to do with the wimpy supply being part of the battery charging protection system, which IMHO is a huge cheat. They relied on the low current supply to limit how fast the battery would charge, instead of doing it in circuit.


Otherwise, for each device, when fed it's rated voltage, will consume no more current than specified, regardless of how much is available, and usually less than specified. This is true so long as there is no fault, which is what fuses are for. :)

Best,
Erik

Another way to think of this is math. The independent values are Voltage and Resistance.
The current flow depends on them.So,


Current = Volts / Resistance

where R is provided by the device being powered, and V out is provided by the wall wart. The current that flues is DEPENDENT on the two values (V & R). Truth is, the current may well be dynamic, and usually less than rated by the device.

While we can re-write this equation a variety of ways, useful when we know only 2 of the values and need the third, in practice this is how we treat wall warts and most power supplies.

I read this:

12V, 1A


in this way:

"I will supply at least 12V so long as my current rating of 1A is not exceeded."

“...when fed it's rated voltage, will consume no more current than specified, regardless of how much is available.”

Thanks erik. This answers the question for me. My comment about the device getting too warm was related to a battery charging system (cordless screwdriver) which you also addressed.