Dynamo's +2 PWR per turn compares favourably with other generators, but the downside is that it generates no PWR for up to 10 turns. The first turns of the mission are particularly critical as they are your opportunity to explore and hack early in the mission before additional Security Cameras are activated, firewalls are raised and additional guards arrive. So, Dynamo's downside can be quite significant. Typically, your PWR in the early mission will come only from Consoles.
This downside notwithstanding, Dynamo is still considered to be a relatively good generator, albeit a situational one which works best within a broader strategy. Dynamo can help with strategies which rely on surviving at high alarm levels, either because of slow movement and hacking, trying to use an Econ Chip at every Console, or killing guards.
Do not fall into the trap of intentionally raising the alarm tracker just to start generating PWR with Dynamo. You will reach alarm level 2 by just waiting enough turns anyway, but you can do other things in those turns while you're waiting; even just letting items cool down can make it better to wait.
Dynamo works well with Parasite or Mercenary, which can hack cheaply but slowly before alarm level 2. Dynamo also generates enough PWR per turn to sustain Archive Prism's Holo Projection Mesh indefinitely.