Why do my speakers save me power?

"I'd say it's unlikely you're truly using less power when they're plugged in than when they're not.

You've commented that you're using the same power when they're off, or not plugged in at all, but the number goes down when you turn them on.

My initial thoughts are that your power meter isn't super accurate near the zero end. If it's anything like the Kill-a-watt units, they claim up to 0.2% accuracy (1% typical), but don't provide a minimum reading.For example, the 110V version says it's accurate to 0.2%, but doesn't say over what range, 0.2% of full scale is about 4 Watt, 1% is 18W.

Things to try.
1. Load the powerboard up with something of at least a couple of hundred fairly steady watts, then plug the speakers in and out and see if the change is the same.
2. Do the same measurements with the audio source connected and disconnected, to eliminate the loading issue."