Another mini piezoelectric air pump. Let's compare the circuitry.

Following on from my very destructive opening of the previous piezo air pump in this video:-
https://www.youtube.com/watch?v=hKsZUuvtylE
I decided to buy another different style for comparison. It's arrived and since we already know what's inside the main pump case from the previous video, let's try it out and then doodle out the schematic of the power supply circuitry.
It's very similar to the first unit we looked at, but replaces the first resistor with a capacitor. It's a bit odd because the other version with three resistors was very simple and possibly more reliable. The combined value of the resistors is pretty much the same anyway.
My theory about the PTC fuse being to protect against capacitor failure or excess electrical noise causing rogue current flow is wrong. It's in series with the capacitor and two resistors that total 24K and would limit fault current in a dead short to 10mA, a third of the fuses rating. The resistors would also just dissipate a worse scenario power of just over a watt each which is well within their rating.
I get the feeling this might be one of many clones with various hashes of the same circuitry.
Someone suggested the theory of the final stage filter being to reduce mains borne signalling noise like data. That's viable, as the piezoelectric disk would act like a loudspeaker and make any noise in the audio range audible.
The disk in the body flexes at 50Hz/60Hz and makes up for the small movement with its area and speed.
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