450 watts with a R9 380 may work, but it will push the power supply hard under full load. 550 watts is recommended for the R9 380. The same goes for the GTX 970, which has similar, but slightly less, power requirements. Most 450 watt PSU's don't have the needed 6-pin PCIe power cables needed by a GTX 970 and R9 380. It looks like you need to upgrade your PSU in either case.