That's a old 400 WOPL build, from before Joe put together his multimedia 400 build montage.
We builders used to run the AC line legs across the top of the left back plane, then down to the thermobreaker.
So, AC was run across the top, DC across the bottom.
And I always felt, the DCP grounds should be in the lower DC bundle, as they all attach to the copper buss bar, aka star ground. This was discussed before at some point, I forget where.