Question about darkness, faerie fire, and blinded (re: (dis)advantage)

So, I got confused by a rules question.  And I don't agree with the explanation I was given at table, based on the RAW.

Disadvantage/Advantage don't stack and they cancel each other out, correct?  So, if 2 sources of disadvantage apply, and 1 source of advantage applies...is it correct to say that the roll is normal, and not at disadvantage?

Scenario: Magical darkness as an aura, but the creature is hit with an upcasted Faerie Fire at 3rd level.  But if you failed the constitution save for this darkness (some special Shar variant), your character gains the blinded condition.  So blinded and darkness both give disadvantage, neither stacking.  And the target has Faerie Fire (which, due to be upcast is not dispelled by the darkness), which gives advantage.  So disadvantage and advantage cancel out and, even blinded, the roll is a 'normal' roll, correct?

As described in the Player’s Handbook, if different circumstances would give both Advantage and Disadvantage in the same situation, the Advantage and Disadvantage cancel out, regardless of how many circumstances would grant Advantage or Disadvantage.

Is my understanding correct here?  I was told that the darkness effect cancelled the advantage from Faerie Fire, but that Blindness would apply disadvantage.  That doesn't appear consistent with the explanation above.  Did they misunderstand this rule, or am I missing something here?  If I'm missing something please advise.

Quote from AzruThazon04423 >>

Disadvantage/Advantage don't stack and they cancel each other out, correct?  So, if 2 sources of disadvantage apply, and 1 source of advantage applies...is it correct to say that the roll is normal, and not at disadvantage?

Correct. You either have advantage or you don't, and you either have disadvantage or you don't. If you have both, then you have neither. The number of different sources of advantage or disadvantage does not have any impact on anything.

Quote from AzruThazon04423 >>

Scenario: Magical darkness as an aura, but the creature is hit with an upcasted Faerie Fire at 3rd level.  But if you failed the constitution save for this darkness (some special Shar variant), your character gains the blinded condition.  So blinded and darkness both give disadvantage, neither stacking.  And the target has Faerie Fire (which, due to be upcast is not dispelled by the darkness), which gives advantage.  So disadvantage and advantage cancel out and, even blinded, the roll is a 'normal' roll, correct?

Correct. If someone told you that you have disadvantage in that situation, they're either using some kind of house rule, or they've misunderstood how advantage and disadvantage work. This is a bit counter-intuitive, so it's not uncommon to find people who either don't understand this or choose to use a different model as a house rule when they're DMing. But if it's the latter, that's something that should be made clear to the players in advance.

If you need a reference, you can find the rules for this in chapter 1 of the Basic Rules or Player's Handbook under "D20 Tests", the subsection labeled "Advantage/Disadvantage" (see here).