What item could this PCB board be from? (NOT serious, misc. question)
What you've got is a switched mode power supply. Mains AC goes in at one end and well regulated DC comes out at the other. There are a few clues:


The obvious one is the switching transformer in the middle and the "no-man's land" beneath it on the underside of the PCB. The combination isolates the low voltage side from the mains.




Figure 1. SMPS block layout. Source: Wikipedia Switched mode power supply.


The red leads at the bottom are the mains input.
The mains is rectified to high-voltage DC by the four diodes beside the blob of goo.
The large capacitors beside the diodes smooth out the rectified AC. The voltage on these capacitors is typically one and a half times the nominal mains voltage and DC. It can hurt or kill!
The 8-pin chip is the switching regulator. It switches the DC supply to the transformer at high frequency - maybe 100 kHz - creating an alternating signal that can be transmitted through the transformer. I can't see it but usually there is a largish transistor to switch the power rather than the chip doing it itself.
On the top of the board we see some more diodes and capacitors to rectify and smooth the DC output.
Finally we need some feedback from the output to increase or decrease the switcher as required to maintain the correct output voltage. The feedback needs to be isolated so the 4-pin opto-isolator on the right of the transformer provides this. Internally there is an LED and a photo-transistor separated by a transparent isolator capable of withstanding 1000 V or so.



  What item could this PCB board be from?


It could be from anything requiring an isolated low-voltage regulated DC supply.