I don´t see how the DFplayer module is getting powered on the NodeMCU picture. It looks like it has its own power supply. It is possible to connect to GND and VIN of the NodeMCU to get 5V from the USB power connector. If, for some reason, you insist on having a separate power supply for the dfplayer module, it is important to have the GND´s of both power supplies connected. Other typical points of attention with dfplayer: the SD card must have max 32Gb capacity and must be formatted as FAT16 or FAT32.