Вот, кстати, об измерении "постоянки" в сети от шефа PS Audio:

"By the way, it is very difficult to measure the DC offset on the power line. Most meters will not do it accurately. On a typical Fluke meter, the input circuits would have to be set to accomodate the full waveform, so there is no clipping on the input stage. So for 120VAC, the meter would have to be on the 200V scale. (169V peak on the sine wave) Most 3-1/2 digit meters are limited to 0.1V resolution on this scale. Also the meter specs usually say the last digit can always be off by one. So, unless there is more than 200mV of DC, the result you measure is pretty meaningless. If you allow the meter to go to the 200mV DC scale, then the input stages are being driven into clipping most of the time, and again the reading is meaningless. (it doesn't tell you that... it will give you a number) A 4-1/2 digit meter will start to give meaningful data, but I wouldn't call it accurate."