...letting me know about the adjustment for that power module and any other sujestions....
You need a DC voltmeter and a small screw-driver to adjust the set-screw of the blue "potentiometer" so that the output voltage is ~5V DC.
GRJ suggested US sellers on eBay. If you don't mind waiting a few weeks for shipping from Asia, you can get the 2 modules (AC-to-DC voltage converter and audio amp) for less than $5 all-in. If there's interest, just say and I'll show how.
Separately, it sounds like some guys have 2 speakers available. If you have the space to install 2 speaker great. Note that the PAM8403 audio amp has the ability to drive 4 Ohm speakers. This can open the door to several options. For example, you can drive two 8-Ohms speakers in parallel (equivalent to a 4 Ohm speaker). OR, since the PAM8403 module is stereo (2-channels left and right) you can drive two 8-Ohm (or two 4-Ohm) speakers separately (one on the left channel, one on the right channel).
Many options to get the job done for just a few bucks.
If you are adverse to soldering, there are audio modules that have screw-terminal inputs and outputs. And so on.