From context, I am thinking your problem is a PSU with a 4 pin CPU power connector and an 8 pin motherboard.
The 4 -> 8 pin CPU power adapters are useless. They don't increase the amount of power the PSU can provide.
If you have a CPU with a TDP of 120 watts or lower, just use the 4 pin plug.
Orient the motherboard so the CPU power plug is in the upper right corner. Depending on the orientation of the motherboard socket:
if the socket is horizontal, use the right 4 pins.
if the socket is vertical, use the lower set of pins.
i repaired a psu once! omg it was epic. i almost blew up. there were sparks everywher, i made the house catch on fire...
IM KIDDING ABOUT THAT!!!
but yes i do sometimes replace the fans in power supplies. past that, i do not recommend you try to fix a psu.