Hi,
The value of if (power.getOutputValue() belongs to HIGH) is not true or false, it is a value between 0.0 and 1.0, where 0.0 is false, 1.0 is true, and the values in between indicate to what degree the output value belongs to the term HIGH. As such, you may want to use some value as threshold:
...
engine.defuzzify();
if (outputVariable.fuzzyOutput().activationDegree(outputVariable.getTerm("HIGH")) > threshold){
//do something
}
does this answer your question?