Source: Expanded Psionics Handbook
You learn another power.
Prerequisite: Manifester level 3rd.
Benefit: Add to your powers known one additional power of any level up to one level lower than the highest-level power you can manifest. For example, a 7th-level psion gains either a new 1st, 2nd, or 3rd-level power. You can choose any power, including powers from another discipline's list or even from another class's list.
Special: You can gain this feat multiple times. Each time, you learn one new power at any level up to one less than the highest-level power you can manifest.