That depends. If it's a top mount psu and you have a large air cooler mounted to your cpu, then no it won't fit afterwards. In that situation you'll have to mount the psu first, then mount the motherboard with cpu cooler attached underneath it. This is also assuming you don't have a cut out in the back panel of the motherboard tray. Even if you do, the air cooler will have to be removed to make room for a top mounted psu in most cases. If it's a bottom mount psu, then you can install everything and put the psu in last.