Enhancements

Reliable (generic version) (+5%/level): The "Reliable" enhancement, described for the Warp advantage in GURPSBasicSetCharacters, adds a +1 to the power's activation roll, for each level of that enhancement. Kromm mentioned on the SteveJacksonGamesForums that it was "safe" to use this enhancement with any other power (advantage). This does not apply to attack powers' aim roll (such as Innate Attack). Spend points in the appropriate skill instead, or in the Accurate enhancement.

Trained (+5%/level): This is really the same enhancement as "Reliable" (see above). It adds +1 to a power's activation roll. The only difference is what it represents. "Reliable" descibes the fact that a power is, well, reliable, whereas "Trained" (or "Experienced") means that the character actually practiced in order to raise his ability to trigger this power.

Limitations

Untrained (-10%/level): This is the opposite of the "Trained" enhancement. Its adds a -1 to a power's activation roll. The same limitations than "Trained" applies here in terms of validity of this modifier. This is different from "Unreliable", as this limitation adds a randomness factor (the power is "Unreliable" because it sometimes fails for no apparent reason). "Untrained" means that this power sometimes fails, but for a good reason: lack of training. You can raise the power's activation roll again later by buying levels of "Trained".