JulianC - I don't doubt that you have seen reduction, but it DOES depend on what the loads are that are connected to the unit. Things like switched mode power supplies are self adjusting, they draw a higher current at the lower voltage, the result is exactly the same ammount of Watts being consumed. SMPS is used for a large number of modern devices in the home (modern mobile phone
chargers, DVD players, LCD TVs, computers, CFL lighting etc.), and the lower voltage will not make any difference to these devices.
On more linear devices such as transformers / ballasts and resistive loads (incandescent lighting, heating elements etc.) there will be a power reduction, along with the associated reduced power output for these devices. So a fluorescent fitting with a magnetic ballast will have a lower consumption (and dimmer lamp), but an identical unit with an electronic ballast will not. Fridge / freezer compressors will see a reduction in consumption, and so will a Microwave oven.
So if a house is full of inefficient loads (no energy saving bulbs, transformer based wall-wart power adapters, older CRT TV etc.), then yes there will be the claimed saving.
The same house with energy saving bulbs (CFL and most LED), few wall-wart adapters that are all SMPS, modern LCD TV, laptop / desktop computer, and NO electrical heating elements (so gas CH + HW and gas cooker / oven), with no washing machin or tumble dryer - then this housewill see
little or nothing in the way of savings.
Obviously I'm not including intermittent loads like the kettle, fridge compressor or vacuum cleaner, but these would also have saving. It would take a long time to recoup your money with just these loads however...
These devices will only work for
some, and not for others, hence the range of views. In my case, I would be wasting my money as
ALL my devices except for the CH pump, fish tank filter pump and my fridge-freezer are SMPS loads. The savings I would see would take MANY years to cover just the cost of the unit alone...
SS