You will not void the warranty if you install a Samsung SSD. If , however, you cause a problem during the installation such as damage to a component they will not cover it under warranty. But it is a pretty straightforward install and you should have no problems or worry about the installation. If you purchase it from Dell they will support it. 
Does Dell support Samsung SSD drives  installed in T3420 Precision Tower?   Will It void my service warranty?   Thanks
DEll support for Samsung SSD drives