I have bought the XH-M543 audio amplifier from Aliexpress. The listing cost is 4.77 EUR, however I bought mine quite a lot cheaper (0.93 EUR) with some discount. The listing claims that the amplifier is capable of outputing 120 Watts on each of the two channels.

The chip according to the listing is TPA3116, but I have not check this, because I did not wanted to remove the heatsink, which is probably attached using some glue. According to the chip datasheet this output ratting seems somewhat dubious. The datasheet states that the maximal output configuration is 50 Watt per channel with 21 Volts power supply and 4 Ohm load.

The PCB seems to be quite simple. The only additional chip is TL074C, which is operational amlifier. There is also polarity protection diode SS54. It has maximum average rating of 5 Amps, which equals to 100 Watts at 20 Volts. This seems to be in line with the TPA3116 real power draw.