I was thinking of changing a wallwart 12v 1000mA PS from linear to SM, as the latter is more efficient, but now I'm not so sure.

What is the no-load power consumption of each type? I understand from Wikipedia that a SWPS must operate with a minimum current, so needs a dummy load when it is not being used.

Also, I have generally assumed that SMPS efficiency is in the region of

70%+, whereas linear efficiency is only 30 - 40%. However, this 1250mA multi-voltage SMPS has an efficiency of only 51%Does that mean there is little point in going to an SMPS if the power consumption if on the low side? Or will it always win out in terms of cost of operation?