Why does the Splitvolt Splitter Switch's power reading seems to be slightly off?

Normally one would assume Power = Voltage * Current.

So why is the splitter switch’s power reading not equal the voltage * current here?

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To explain the reason for the difference in your calculation, we have to talk about power factor.

Power factor is a measurement of how effectively electrical power is being utilized in an AC (alternating current) circuit. It represents the ratio of real power (measured in watts) to apparent power (measured in volt-amperes or VA) in the circuit.

In an AC circuit, the voltage and current waveforms are not always perfectly in phase with each other. This phase difference is caused by the reactive components in the circuit, such as inductors and capacitors, which store and release energy in a cyclic manner. Reactive components can cause the current to lead or lag behind the voltage waveform.

When the current waveform is perfectly in phase with the voltage waveform, the power factor is 1, indicating that all the supplied power is being used for useful work. This is called a unity power factor. However, in many practical situations, the current waveform is out of phase with the voltage waveform due to the presence of reactive components, resulting in a power factor less than 1.

The power formula, P = V * I, assumes an ideal scenario where the power factor is 1. However, when the power factor is less than 1, the formula needs to be adjusted to take into account the power factor. The adjusted formula is:

Real Power (P) = Apparent Power (VA) * Power Factor

To calculate the real power in watts, you multiply the apparent power in VA by the power factor. The power factor essentially tells you how much of the apparent power is being used to do useful work. A lower power factor means that a larger portion of the supplied power is being wasted or lost as reactive power.

By considering the power factor, the calculation of power accounts for the inefficiencies and losses caused by the reactive components in the circuit. It provides a more accurate representation of the actual power being consumed or delivered by the electrical system.