My computer runs on a normal 120v plug at 1000w at the wall which is about 8.5 amps. the PSU works on 240 and 120 so i decided to plug it into a 240 outlet i use for homebrewing and it only pulls 4.2 amps now, i cant tell watts because my wattmeter is only good for 120v so i just used my amp clamp on the multimeter. So if I'm pulling half the amps does that mean my power usage at the street is lower? Like would my power bill go down if i started using 240 for all my dual voltage electronics?

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    Amps are half, but voltage is trice. Amps x volts = watts. Watts x time = power cost(most times)
    – crip659
    Commented Apr 9, 2021 at 21:50
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    What is 120 x 8.5? What is 240 x 4.2? Commented Apr 9, 2021 at 23:10
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    Measurement error will be higher than the actual difference.
    – Ed Beal
    Commented Apr 9, 2021 at 23:37
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    The same amount of work requires the same amount of energy, it doesn't matter whether you are using wind, solar, tidal energy, hamsters, a natural gas turbine spinning a generator, 120vt, 240vt, 480vt... You don't get something for nothing. Commented Apr 10, 2021 at 0:25

2 Answers 2


Power equals amps times volts, and for all practical purposes is exactly the same, other than measurement error.

Twice the volts, half the amps, same power.

That's a very power hungry computer by modern standards - there, there's real room for potential savings by using a more power efficient computer.

  • How do you feel about I*R losses being reduced at higher voltage?
    – fred_dot_u
    Commented Apr 9, 2021 at 21:53
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    For a computer power cord and the wiring leading to it? Like it fails to add up to a meaningful amount unless you happen to be 1000 feet from the breaker panel...very unlikely to produce a noticeable change in your power bill in a normal size house.
    – Ecnerwal
    Commented Apr 9, 2021 at 21:56
  • ohhhhhh ok it just seemed like i was using less power since the amp draw was lower. And its a high end custom made gaming/editing rig with 3 GPU's.
    – rasmukri
    Commented Apr 9, 2021 at 22:01
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    3 GPUs and worried about power? Tell the truth, you are mining. A high end gaming computer doesn't need 1000 watt PSU.
    – Gunner
    Commented Apr 9, 2021 at 22:16
  • It has a 1600w PSU it pulls 1000w. I have a mining rig yes, but this particular machine is my main rig.
    – rasmukri
    Commented Apr 10, 2021 at 5:05

In the case of electronics that convert the voltage to a lower voltage in both cases not really the wattage is the same p= I x E double the voltage and 1/2 the current so no it won’t make a difference.

With motor loads a dual voltage motor is usually slightly more efficient at the higher voltage but it’s not a large amount as 746w = 1 Hp again double the voltage 1/2 the current.

Basically the only difference will be in how efficient the conversion from 120v or 240v to the the different low voltage DC values used by the computer.

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