The only other thing affecting the player's maximum Psi Points is unlocking main Tiers of Psi Powers.Maximum Psi Points of the player change when upgrading the PSI stat, but they are not affected in any way by the items, RPA, nor overloading.Psionic Ability vs maximum Psi Points Table Psionic Ability Level The amount of bonus Psi Points given depends on the difficulty:

Psionic Ability increases the Psi Points of the player and influences the duration/effectiveness of Psionic Disciplines. It is not possible to reach PSI 9 or 10 without Overloading. Overloading a Psi Power casts it with a bonus of +2, to a maximum effective PSI of 10 (player needs to have PSI 8 already before casting to reach PSI 10).

Recursive Psionic Amplification (RPA) (+2).

The player can only permanently upgrade Psionic Ability to level 6, while the next two levels require a combination of the following items/ Psionic Disciplines: The maximum effective Psionic Ability level is 10, although most Psionic skills benefit from a PSI up to 8.

Psionic Ability or PSI is one of the basic statistics in System Shock 2.

System shock 2 patch SCP