You'd be best off selling the two sticks of ram and picking up a dual channel ram kit. You're also better off with a DDR4-3200MHz ram kit, to eek out that performance from your platform. If you don't know what you're looking at on the SPD tabs, the two sticks of ram are from two different kits(that's like having two different sized clown shoes). The lack of any VRM heatsinks on the motherboard does leave a lot more doubt(the same as the PSU) but you're pending BIOS updates. Gradually work your way to the latest BIOS version taking note of any MEI firmware updates as you update the BIOS.
So in short your "performance" losses are not just confined to your PSU...you forgot OS version.
It does run still, but I believe that the PSU is on it's last legs.
Like I said you don't understand, that PSU shouldn't have any legs, not when the parts in your system want more than what the PSU can deliver. In fact, it should be 6 feet under considering it's a second hand unit.