A surge of power is a special event in ADOM. Upon entering certain levels (exceptions: the piranha lake level, the Bug Temple cave etc.) for the first time, some items will be generated on the floor. If one of these items is an artifact, the player is alerted by the message "You feel a surge of power." and a "(more)" prompt.
When an artifact is generated as a random item, a named monster is also generated near the item — referred to as an 'artifact guardian'. The guardians tend to be higher leveled than most other monsters on the same dungeon level.
Surges of power are generally a very rare occurrence. Players that have explored every level in the game may find one or two of them; but it is not uncommon to find none at all in a completed game. It is not known if certain levels have higher chances of generating them; they are reported to be exceptionally rare in the Village Dungeon, and usually more common in the Small Cave.
The race of the chosen monster appears to be completely random; undead creatures like shadows and vampires have been spotted, as well as barely-sentient named monsters such as an eye of destruction. Seemingly, a vortex may even appear as an artifact guardian; this may be a concern for early game PCs as high-leveled vortices are bound to explode with devastating force. Having at least two sources of resistance to the corresponding element is vital.
According to the official ADOM FAQ, "(a)rtifact guardians are scaled to be more appropriate to the object they guard". The actual relationship between the artifact generated and the level of the guardian is not yet certain.