Want to know what psu and mobo I need

I've updated your build:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Core i5-8400 2.8 GHz 6-Core Processor ($184.99 @ Amazon)
CPU Cooler: Cooler Master - Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($27.89 @ OutletPC)
Motherboard: MSI - B360 GAMING PLUS ATX LGA1151 Motherboard ($89.98 @ OutletPC)
Memory: Corsair - Vengeance LPX 16 GB (2 x 8 GB) DDR4-3000 Memory ($104.99 @ Amazon)
Storage: Samsung - 860 Evo 500 GB 2.5" Solid State Drive ($84.99 @ Amazon)
Video Card: Gigabyte - GeForce RTX 2070 8 GB WINDFORCE Video Card ($492.28 @ Walmart)
Power Supply: EVGA - SuperNOVA G3 650 W 80+ Gold Certified Fully-Modular ATX Power Supply ($79.00 @ B&H)
Total: $1064.12
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-02-01 12:24 EST-0500

I'd have to disagree with SR-71 a little here. The 8400 is actually a really decent CPU, and is not too shabby a gamer. It holds it's own against more powerful CPU's like an 8600k/8700k, and is only about 10% difference performance wise in FPS when compared to the 8700k, sometimes less. IMO it will drive the RTX2070 just fine, for the most part.

There are very few games that use more than 6 cores or threads. There are one or two games like BF V for example, that can make use of more cores/threads, but with the 6 on the 8400 you would still have a really good gaming experience. With pretty solid high FPS and in game settings. In a year or two the 8400 will start to max out, and you could look at an I7 as an upgrade for more longevity.

edit: have a quick look at tom's review here: https://www.tomshardware.com/reviews/intel-coffee-lake-core-i5-8400-cpu,5281-4.html

This review is with a GTX1080 which is a similar level card to the 2070. You can see the 8400 is pretty competitive.
 
Possibly game specific, as opposed to all games? The 9600k has a much higher base clock, which possibly really helps, but overall for most games the 600mhz difference in max boosts clocks, would literally mean anywhere from 5-10 fps difference between the two CPU's, like 10%, at 1080p.

I'd defo agree the 8400 is a budget-midrange CPU. It just so happens at 1080p it beats the pants of a lot of Ryzen 2xxx CPU's and is very competitive with even a 9600k.

I hate posting videos for comparison, but hey, it's Friday :) :https://www.youtube.com/watch?v=R4ycNeKM6Nk

The difference between the CPU's FPS wise is nearly 100% due to faster turbo speeds, and IPC increase of the 9600k. With the same number of cores/threads. It's not about a bottleneck really. IMO.