CPUs you can use with a 400W PSU

Assuming you already have a ~75W GPU, here's a compiled list of possible CPUs you can use:

CPU	TDP	Quick Buy
AMD Ryzen 5 7500F	65W
AMD Ryzen 5 5500	65W
AMD Ryzen 5 5600	65W
AMD Ryzen 7 5700X	65W
Intel Core i5-12400F	65W
AMD Ryzen 5 5600G	65W
AMD Ryzen 7 5700G	65W
Intel Core i3-12100	60W

What CPUs can you use with a 400W power supply?

First of all we have to make an assumption regarding the rest of your PC, let's start by assuming you have a ~75W GPU. Also, we can assume that the rest of your PC components (MB, RAM, Fans, Storage, etc...) consume an additional 100W, and we'll have an additional 100W of margin. That leaves us with 85W for the CPU.

With 85W you can squeeze in CPUs such as AMD Ryzen 5 7500F, AMD Ryzen 5 5500, AMD Ryzen 5 5600, AMD Ryzen 7 5700X, Intel Core i5-12400F.