Not-so-Random Encounters is a 5th Edition supplement for 3-7 characters of 7th-level and is optimized for four characters with an average party level (APL) of 5 or 8. This document offers details for each level and makes adjustments accordingly. This supplements provides a dozen random encounters for any dungeon setting.
Random encounters can be a great way to challenge the party in interesting ways, but they can also have the effect of slowing down the pace of a session, so use them at your own discretion. Here are three reasons I use them.
Ninetoes82: 5E Adventures, Encounters and More 