True PSU - SMPS 900 Watts

What upgrade do i do to speed up my old desktop pc and laptop ?

Most Importantly, Upgrade your HDD to SSD. SSD is theoretically 12 times faster than a normal HDD and when you replace HDD with SSD the workflow of your system speeds up by say around 3 times. So your same configuration will work like a next level machine, i3 will work like an i5 machine.