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Weird
I noticed my 144 watt can opener becomes a 38.4 watt can opener while using an inverted?
Is there something in error here?
Is there really that big of a difference when it comes to dc and Ac?

It is probably rated at 144 watts under full load. Heavier cans or thicker metal will cause it to draw more power. A motor draws more current as needed as the load increases.