While a ‘B’ series is perfectly adequate, the ‘X’ series’ have added PCI lanes that can be helpful.
As far P/S wattage goes: I’d wager that more than one sim user experiences CTD’s and other instabilities because they bought a cheap power supply with ‘just enough’ wattage. Keep in mind that rated power draws don’t take into account instantaneous spikes.
Certainly it’s better to buy a high quality P/S that is closer to the total power draw than a cheap one with higher wattage - along wiith jitter, cruddy capacitors, and unstable transformers.
OP was looking at a 9950X3D, so he’s not looking for a low budget system.
High quality 1000W and X670E. That’s my story, and I’m sticking with it. 