The be quiet! power supply System Power 10 (450 W) is compatible with the ASUS PRIME B250-PLUS Intel® B250 LGA 1151 ATX motherboard. This ATX-format power supply provides a total power of 450 W with 80 PLUS Bronze certification, which is enough to power a system with an Intel i7 7700 processor, 32 GB DDR4 RAM, and an RX 6400 graphics card, provided that the system's total power consumption does not exceed this power.

The power supply has the necessary connectors, including a 20+4-pin ATX connector for the motherboard, an 8-pin (4+4) EPS connector for the processor, and two 6+2-pin PCI-Express connectors for the graphics card, which is compatible with the RX 6400.

However, you need to check that the total power consumption of all the components (processor, graphics card, peripherals) remains within the 450W limit supplied by the power supply. The RX 6400 is an entry-level graphics card with moderate power consumption, so this power supply should be sufficient for standard use with an air case and the components mentioned.

In short, this power supply is suitable for your ASUS PRIME B250-PLUS configuration with i7 7700, 32 GB DDR4 and RX 6400, provided that the total power consumption does not exceed 450 W.