B450 motherboards are not a good pairing for the Ryzen 9 5900X. While the B450 chipset does technically support the Ryzen 9 5900X, it would be unwise to pair the two together. B450 is a budget-oriented lineup of motherboards that do not have the power delivery capabilities to handle the Ryzen 9 5900X. Even the most well-built B450 boards will have trouble handling the Ryzen 9 5900X at stock settings, so it would be best to pair the 5900X with a premium motherboard from the X570 chipset.