Yep, makes sense that it would be completely potted to keep moisture out (you had one job...
)
All that should be in it is 4 diodes. Doesn't look big enough to have a voltage regulator. There's no voltage output from the rectifier when you plug it in, right?
Typically, the LEDs will be in series, or two parallel lines of leds that are in series. Rectified 110vAC will be around 150vDC. Each led drops a couple volts, and somewhere there's a current limiting resistor. 50 leds x 3v each is around the 150vDC they would see. Giving it 9v
shouldn't be enough to get them to turn on at all.
But, if they're color changing there has to be something special somewhere? Although that can be built in to each individual LED too.
Looks like this set?
https://www.amazon.com/Lawn-Lights-Illuminated-Decoration-Multicolor/dp/B07VMKPN8Y/ref=sr_1_2I would be tempted to get a full bridge rectifier, and wire it in place...
