This is a small salvaged rectifier - I do not have a clue about its source, any small home apparel could be!
A couple of pictures:
On the secondary it features a rectifier bridge with an electrolytic capacitor, no more fancy features! The diodes, 1N401, have a nominal capacity of 1A, so that's the nominal intensity of the machine. For an output voltage about 10 V, that's approx. nominal 10 w. The capacitor is rated at 16 V, so little margin.
The circuit, modeled in QUCS, is here.
Crest Factor = (Vpeak/Vrms) and for a sine wave, the crest factor is sqrt(2). Then, if Vrms is 225, Vpeak is 315 V, as in the model.
My DMM has read 8.2 Vrms on the secondary, while the simulation shows a sine wave with a peak-to-peak amplitude of (-0.79,+11.8) V.
The Vrms of this voltage is:
Vrms = (11.8+.79)/2 + (11.8+.79)/2/sqrt(2) = 6.3 + 4.5 = 10.8 V
So, what's wrong?
It is possible that my DMM (Promax FP-2b) is deriving the rms value from average or peak values, which might be not correct for a dc-shifted wave.
Not clear... will have to check with the scope if the secondary is behaving as shown in the model.
I have checked with my USB oscilloscope and the results at the secondary are:
And at the load probe:
4 Inverting the Rectifier
What would happen if the voltage source is placed at the output?
5 Removing the Capacitor
If the capacitor is removed, the output shows a superimposed AC wave of 2.9 V of amplitude.