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When powering household devices, does a power adapter have a preset (or in some cases user-defined) voltage, while the device (while turned on) "selects"/draws whatever amount of amperage it needs at any given time?

Part of why I ask is while searching for replacement power adapters for speakers, one device says it needs 6V DC input and also says max power input is 4W. The adapters I find online have labels with a max amperage listed but a set voltage or selectable voltage. This makes me think amperage can vary based on device use, but voltage is set by the adapter; the voltage needs to be correct but the ultimate power draw can be limited (to under 4W, or with 6V that'd be ~500mA) as needed by the device. Is it the case that an adapter sets voltage but amperage can vary based on device needs/"request" of electricity?

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Yes, most sources of power are constant voltage where the load determines the current. You'll want to get an adapter that supplies the right voltage, and at least add much current and/or power as the load will require.

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Saying that a device "selects" the current it needs is a bit strong -- it implies that there's a brain in there.

But yes, by and large the wall wart acts like a voltage source, and the device draws current depending on the applied voltage and the device's characteristics.

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  • \$\begingroup\$ I have a power adapter that actually lets the user select the voltage (kind of like amazon.com/Universal-Voltage-Switching-Selectable-Suitable/dp/…) \$\endgroup\$ – cr0 Dec 8 '18 at 3:45
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    \$\begingroup\$ while both answers were right alex beat you to it by a few seconds so I'm marking that answer correct. thanks anyway! \$\endgroup\$ – cr0 Dec 8 '18 at 3:55

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