If you are talking about DC offset at amp spk output, yes you can measure it using multimeter set to DC range, what ever DC you measured is the DC offset.
But if you are talking about DC offset at AC supply, I don't think such issue exist in AC circuit. The article you attached is giving wrong information to sell the product.
Typical for AC supply, you will have phase lead or lag issue depend on whether you plug in a lot inductive circuit like big motor... that will change the power factor of AC power supply, so some audio product are actually capacitor that you plug into your receptor that will improve this condition.