There are many Inspiron 3670 with RTX 2000, 3000 series on benchmark site You need a 24-pin to 8-pin adapter cable in order to use an ATX power supply.  Review this upgrade video for more idea. Suggested 450w power supply for RTX 2070.  There are variant brands and sizes cards, select one with proper chassis fitment.  
Is it possible to use NVIDIA GeForce RTX 2070 in an Inspiron 3670? Is there a PSU I can upgrade to that has enough power and works with it?
Inspiron 3670, GeForce RTX 2070 with PSU upgrade?