What power supply you need is directly related to what graphics card you decide on. Picking a power supply should be done AFTER you know what the full system consists of so that you know what kind of capacity is going to be required.
As to the build, if you are going with something like the 1660 TI, then something like the Ryzen 5 3600 would be a lot better balanced. There is no need for a CPU like the 3700x with a lower tiered graphics card like the 1660 TI unless you are shooting for a very high FPS margin due to a high refresh rate monitor, and are playing seriously demanding titles.
A lack of balance usually results in spending money needlessly. Now, if you're going with something like the 2060 Super or higher, and you'll be using a 144 or 240hz display, then a higher end CPU might be a good idea.
Really, it would be best to know your budget for the full build, exactly WHAT you intend the system to be used for including will you be planning to run non-gaming applications, or will you be recording, streaming or other form of heavy multitasking WHILE gaming. These are the things that should determine your build.