You can indeed. The 3477 Supports a 2.5" SATA SSD and an M.2 NVMe/PCIe SSD.
I'm looking to add a second drive (250Gb SSD). I have a 1Tb HD and boot up and OS is slow. My question is can this unit support this and can I have the SSD as my primary boot drive and my HD secondary? If not, I'll just purchase another AIO.
Inspiron 3477 AIO Add 2nd HD (SSD) to Existing 1Tb HD