Yes, that schematic is exactly correct, except the BAT_MON section. it's not needed as we can assume battery is always connected (it also charges from the PSU with a buck converter when PSU is connected, similar to a how a laptop works). and yes, battery is always lower voltage than PSU (2S lipo, so maximum of 8.4V). As I mentioned the battery fets are on as default. as soon as the voltage on PSU_MON is detected (it still can't feed anywhere, mosfets are disconnected). the MCU switches off the BAT_CNTRL fets and a few mS later, it turns on the PSU_CNTRL fets. using this "break before make" (if you will) approach we can ensure nothing ever back feeds as the two sources are never on at the same time! as I explained, I just need enough capacitance on the whole circuit (not only in parallel with Rload as you drew it) to allow the MCU to stay on while making this switch over where there is no power from either the battery or the PSU.