The saving claimed can never really happen, however AC can transfer power by inductive and capacitive linking, which is why every AC LED bulb has a resistor to leak some power around the LED's to stop them either staying on dim or flashing, if we look at the lumen per watt of DC bulbs designed for caravans and boats they are far better to standard household types.
The problem lies in the main with the way we wire lights, the neutral should follow the same route as the line, but we take line only from lamp to switch, so there is some transfer in the switch cable, specially with two-way lighting, with a 100 watt bulb having 0.1 watt loss was not really considered as a problem, with a 6 watt bulb however the % loss is greater.
But the resistor to stop the lamp flashing is built into the bulb, so even if you rewired ones house, so neutral did follow the line, you are still using the same bulbs. Look at the watts total and lumen total for 8 x 5 watt bulbs, and a 40 watt bulb and the 40 watt would be far better, as every bulb leaks the same amount be it 2 watt or 20 watt.
So there may be an odd device where it could help, but like the voltage optimiser very few devices today would it help with, as the power supply to most devices turns AC to DC, then stores it in a capacitor, removing all spikes, then turns it back into AC at a high frequency, then transforms the voltage to voltage required, then back to DC, and it measures the DC voltage and adjusts the mark/space ratio on the electronics making the high frequency AC to keep the volts within required parameters. By time this is done, any spikes are long gone.
The power supply was developed for the front loading VCR machine, the old type power supply produced too much heat, since then it has been used in nearly every device reducing heat and so waste. Even AC devices like fluorescent lamps used the switched mode power supply idea so today even DC bulbs use it, which is how they can work with 10 to 30 volts input. So one may find the odd thing where they can help, but the savings claims are clearly not possible in a normal house, basic fact is everything we plug in uses power, so using a smart adaptor to turn a 20 watt item on/off may save money as it runs for less time, but use it to turn a 1 watt item on/off, likely used more to power the smart adaptor than it saves.
Anyway time I milked my snakes to get the oil out of them.
