Is it a good idea to connect PC to a non-isolated DC supply
It's never a good idea to touch and perform experiments on any non-isolated supply.
You might get an electric shock. Also, in case of occurrence of a mainline fault or some voltage surges, your computer, and the microcontroller too can get hanged or eventually damaged too.
Thus, never work on a non-isolated supply. It's always better to use some sort of isolation transformers to be in safe working premises.

Thanks!