Cycle
Cycle is a passive generator program which resets your PWR to 3 at the start of each turn, except for the first turn of the mission. It can be bought from some Server Terminals for 750 credits.
Cycle's effect always triggers before other passive generator programs at the start of the turn, but it triggers after Distributed Processing and Portable Servers, erasing any PWR they generate.
Cycle is found in the Contingency Plan DLC.
Strategy
Cycle's 3 PWR per turn compares favourably to most other generators, but it has a significant downside: when playing with Cycle, you cannot store PWR between turns, so any PWR you generate but don't use is wasted. Like Charge or Overdrive, Cycle is highly situational and requires the rest of your loadout to fit the play-style required to benefit from it; but since you don't find Cycle until you have already chosen a loadout, this usually means you shouldn't take it.
When playing with Cycle, anything that costs more than 3 PWR can only be done on the same turn you generate additional PWR for it; so you should not have too many high-PWR-cost programs, items, weapons or augments such as Hunter, Volt Disruptor II+, Flurry Gun, Subdermal Cloak or Derek's Transport Beacon. This can be mitigated by having another generator, particularly Emergency Reserve which should consistently generate an extra +5 PWR every three turns with Cycle.
To make Cycle work, you will want to leave Consoles un-hijacked (and drones un-stolen-from) in order to take the PWR later when you actually need it, and you will want to find devices fast enough so that you can use excess PWR instead of wasting it. Particularly on the first turn of the mission, you must explore quickly to find enough devices to hack using your starting 10 PWR (or 5 PWR on Expert Plus mode), otherwise you will lose it. Having Internationale on your team helps a lot with this, since her Wireless Emitter augment detects devices to hack on turn 1, and she can remotely hijack Consoles that you left for later, without moving all the way back to them.
In addition to making Distributed Processing and Portable Servers completely worthless, Cycle also erases any PWR generated during the enemy turn, such as from Archive Internationale's Network Siphon augment, or Olivia's Ambient Turbine augment when ambushing. It is still possible to benefit from these augments by intentionally triggering them during the player turn.