If I get this right afe_pwr_n switches the 12V supply on the board. Sadly I dont understand much from the gateware/software. afe_pwr_n gets mentioned twice, but if I guess right, the first mention is a definition of a message and the second applies the content of the message https://github.com/quartiq/fastino/blob/d451a0e88b3302b5f1a7f5e6c1ef48f7a109ab10/fastino_phy.py#L199 So I dont see the state after a reset there.
The DAC by itself has a default state: "The AD5512A/AD5542A have a power-on reset function to ensure that the output is at a known state on power-up. On power-up, the DAC register MSB is 1 and all other bits are 0 until the data is loaded from the serial register. However, the serial register is not cleared on power-up; therefore, its contents are undefined."