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?
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.
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.