I want to power a monitor using a 12V car battery.
My monitor uses 19V and 1,5A of power and it includes an AC power supply. However, I don't want to transform my 12V into 110 or 220V and then let the power supply transform it back to 19V again, because that would be stupid I think. So I found a power supply which converts 12V into 19V and it has the proper connector, but says it can output 4A. Therefore I wonder: will this power supply burn my monitor, because it supplies 4A, or will the monitor make sure it will only draw as much as it needs (1,5A)? So is it safe to use a different power supply with a monitor?
Answer
Yes, as long as it supplies the 1.5Amps at the 19Volts plus a bit more (surge) current (Amps) for any startup, charging caps and all, and it will work fine. As long as the voltage is correct, the device will only draw the amount of power (current) it needs.
With notes that some DC-DC circuits might not be as clean as the monitor's own power supply would be. Some DC-DC "adjustable" voltage circuits will only supply their theoretical maximums at specific voltages, not the whole voltage range, so if it is adjustable voltage it might not be 4A real, but 4A maximums.
It is (actually) a good idea to have a higher current converter (of the correct voltage) that would be able to cope easily with the smaller current draw, without overheating and being even less clean power (versus maxing out the capabilities of the design).
It is a good idea to have less conversion like you are trying to accomplish, less losses, but you may have more to learn about power driving a specific device beyond some few specs, and the nuances of a particular curcuit.
Sometimes a curcuit requires an additional heatsinking of the mosfet for the high output, an added output capacitor would make the output cleaner.
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