$400 Gaming PC
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CPU
Ryzen 3 4100
4 cores, 8 threads
max clock of 4Ghz
Great for modern gaming and productivity tasks.
Motherboard
MSI A520M-A Pro
2 DDR4 Slots
A solid, reliable motherboard for a starter gaming PC.
Power Supply
Enermax CYBERBRON
500 Watts
80+ Bronze certified
More than enough power for this build. Leaves a good amount of room to upgrade any part (within boundaries of TDP).