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I have multiple ac-dc adapters, one with variable voltage and the others for electronic devices. written on them they give specific voltage and current, How come? Doesn't the current change with the applied resistor?

For those adapters of electronic devices may be the resistance of the device is constant. but for that adapter I bought with variable voltages how it says it gives specific current? It says

OUTPUT: 1.5-3-4.5....V CURRENT: 500 mA

Tito Tito
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The current rating on a power supply is the maximum current the supply is designed to provide. The load you connect to the supply will only draw the current it requires.

The supply you mention can deliver up to 500 mA at any of the voltages specified. The actual current delivered will depend on the requirements of the load.

Peter Bennett
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  • so, What if I connected VERY SMALL resistance, how would it still obey the rule V=IR. How it would compensate for the higher current? – Tito Tito Apr 05 '14 at 18:47
  • @TitoTito I = V/R where R is whatever you attach to it, since V is fixed. However, if I would be greater than 500mA, then behavior is undefined (V may drop, may start pulsing, could blow a fuse, etc.). – Spehro Pefhany Apr 05 '14 at 18:53
  • so, adapters with higher output current are ALWAYS better?are there specific usages for the low current output adapters that can't be used by the higher output adapters? – Tito Tito Apr 05 '14 at 18:58
  • Better? Higher output can mean more noise on the supply. – Andy aka Apr 05 '14 at 19:00
  • as long as it drains the required current. for example, what's the difference between 500mA and 1A adapters, if I connected both higher resistors that always drains less than 500mA? – Tito Tito Apr 05 '14 at 19:04
  • Regulated adapters- little difference. The high power type might waste a bit more power. Unregulated adapters might have ab excessively high output voltage when lightly loaded. – Spehro Pefhany Apr 05 '14 at 19:46