I know the pass without trace spell is strong, but it seems absolutely ridiculous if characters can add +10 to their already high Stealth bonus. For instance, with a Stealth bonus of +8 (which is perfectly achievable for a rogue), you can not physically roll a total below 19 on your Stealth check.
Is the +10 Stealth bonus of pass without trace in addition to the character's existing Stealth check bonus?
Best Answer
Yes, pass without trace adds to the character's existing Stealth check
The pass without trace spell description says:
The spell doesn't say it replaces your existing Stealth check modifier; therefore, it is added on top of it. And as long as two game features don't have the same name, their benefits stack on a target. (In this case, there aren't even two different features or abilities being stacked; it's simply one bonus stacking on top of the default/existing bonus.)
It's not without limitations
Note that the spell description only says it adds a bonus to your Stealth checks and prevents you from being tracked after the fact; it doesn't make you invisible, totally inaudible, unsmellable (as Jeremy Crawford clarified on Twitter), or impossible to detect using other senses.
In addition, the spell description says that it grants those benefits to targets within 30 feet of you. Crawford clarified on Twitter that it's intended to benefit creatures only while they stay within that radius of the caster, though the caster can choose different targets over the duration of the spell.
In other words, the party will still need to stay out of sight - they'll still need to follow the rules for hiding. If the enemy's on the lookout for the party, the party will need something to actually hide behind; if they just stroll out into the open, the enemy will notice them, spell or no spell.