a As per the specs here, 48 GB is not listed as a compatible configuration. Will it work, possibly. Also make sure the RAM is compatible. Mixing RAM makes never is a good idea with Dell and generally Crucial RAM seen here is the most compatible.
Hello Gang Precision 3620 i7 7700 4.2 GHz Is it possible to combine #2 sticks of 16GB (32GB) with existing #2 sticks of 8GB (16GB) for a total of 48GB? Mushkin Essentials – DDR4 Desktop DRAM – 32GB (2x16GB)  Thank You!
Memory For 3620 - Combining 2x16 (with) 2x8 Total 48GB