Regulation stating a type AC RCD can not be upstream from a type A RCD

I am now going to reply to Andy J. The design of modern SMPS does not have a rectifier into a smoothing capacitor because the "rules" say they must achieve virtually perfect power factor. The rectifiers feed the first switch mode stage which chops up the rectifier output throughout the cycle so takes a sinusoidal current in phase with the supply. Thus good power factor. What happens after that is conventional. Small consumption appliances do not need this stage because there is a limit to the requirement in terms of power but an 800W microwave with a SMPS would have to comply. Essentially we have a load which must take equal current from L and N whatever happens to it's output, the mains cannot have a DC component! A fault to Earth would simply cause more mains consumption, not DC! The Earth wire might carry DC, but that does not flow as DC through the RCD, simply in the Earth-supply TX N loop, which is not seen by the RCD! Interesting, try sketching a circuit diagram, there is a double wound transformer in the way in the appliance. Until someone makes a complex SMPS without a transformer there is basically nothing to worry about, as long as it is not possible to contact the DC output and the class 2 transformer is not faulty, even if it does operate at 100 kHz or so. You do need to realise that an Iphone charger or similar has this class2 transformer, but it is very small due to the high frequency of operation.

I am now going to reply to Andy J. The design of modern SMPS does not have a rectifier into a smoothing capacitor because the "rules" say they must achieve virtually perfect power factor. The rectifiers feed the first switch mode stage which chops up the rectifier output throughout the cycle so takes a sinusoidal current in phase with the supply. Thus good power factor. What happens after that is conventional. Small consumption appliances do not need this stage because there is a limit to the requirement in terms of power but an 800W microwave with a SMPS would have to comply. Essentially we have a load which must take equal current from L and N whatever happens to it's output, the mains cannot have a DC component! A fault to Earth would simply cause more mains consumption, not DC! The Earth wire might carry DC, but that does not flow as DC through the RCD, simply in the Earth-supply TX N loop, which is not seen by the RCD! Interesting, try sketching a circuit diagram, there is a double wound transformer in the way in the appliance. Until someone makes a complex SMPS without a transformer there is basically nothing to worry about, as long as it is not possible to contact the DC output and the class 2 transformer is not faulty, even if it does operate at 100 kHz or so. You do need to realise that an Iphone charger or similar has this class2 transformer, but it is very small due to the high frequency of operation.