[Piotrsko]

If the yellow transformer is across the AC plug, they are isolated, that is why the transformer is there. It's cheaper to build a buck power supply that is transformer less but not isolated. The diodes are getting hot because you are running max current the device was designed for, ditto on the capacitors because they are supplying current during the "off" portion of the cycle. I wouldn't run more than half the rated current without having heat sinks if you want any longevity or "surprise" oops events.

I would also be inclined to use the modules as is with the bms on top if they allowed charge to 4.2 @ cell. Which gives you 12.6v