A system (40) includes a first powered apparatus (42) having a first analog signal (16) with a fundamental frequency (ω o ); and a second apparatus (44) providing load diagnostics or power quality assessment of the first apparatus (42) from a second digital signal (I F (n)). The second apparatus (44) includes an input (46) of the first analog signal, an output (48) of the second digital signal (I F (n)), a processor (22), an adaptive filter (50) executed by the processor, a digital-to-analog converter (20), and an analog-to-digital converter (10). The adaptive filter routine outputs a third digital signal (y(n)) as a function of the second digital signal (I F (n)) and plural adaptive weights (4,6). The digital-to-analog converter inputs the third digital signal (y(n)) and outputs a fourth analog signal (I o est(t)) representative of an estimate of a fundamental frequency component (I o (t)) of the first analog signal (16). The analog-to-digital converter inputs a difference (I(t) - I o est(t)) between the first and the fourth analog signals (I o est(t)), and outputs the second digital signal (I F (n)) representative of the first analog signal with the fundamental frequency component removed.