Uhm, there's not an existing post that I know of...

There's a sliding scale based on the quality of the planet to how many increases it can have.

Dead asteroids are obviously the weakest
Terrans are the best

IIRC the order is
Dead
Asteroid
Volcanic
Ice
Desert
Terran

Depending on which race you play there are different techs to increase population caps. TEC, for example, get abilities that increases max population on Terran, Desert and Ice (do they get a Volcanic increase as well? Don't think so). Advent (which I have been playing since launch) get major upgrades to Desert pops, increases to Terran pops but no increases for other planet types.

There are also the planetary abilities that increase individual planet caps, don't ignore those. The first one(s) will negate tax losses and later ones increase max population so they generate far more taxes (fully tricked out Terran planets will produce 10+ income per second by themselves).