[RPG] Do you have advantage when multiple sources give advantage and only one gives disadvantage

Yes, A DM could impose disadvantage and grant advantage on the same contest.

There is precedent for it. The Cloak of Elvenkind grants both advantage and disadvantage to a Wisdom (Perception) vs Dexterity (Stealth) contest. From the SRD:

While you wear this cloak with its hood up, Wisdom (Perception) checks made to see you have disadvantage, and you have advantage on Dexterity (Stealth) checks made to hide, as the cloak's color shifts to camouflage you. Pulling the hood up or down requires an action.

It is therefore possible to imagine other situations in which a Dungeonmaster could grant similar concurrent bonuses/penalties. Note that items which do this are very few. A ruling such as this based on a current situation should be just as rare. Advantage vs Disadvantage contests are pretty much a foregone conclusion, and almost beg the question "why bother to roll?"

Inspiration gives you advantage(PHB, 125):

If you have inspiration, you can expend it when you make an attack roll, saving throw, or ability check. Spending your inspiration gives you advantage on that roll.

But, as you know, if you have both advantage and disadvantage, you count as having neither(PHB, 173):

If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them, and you roll one d20. This is true even if multiple circumstances impose disadvantage and only one grants advantage or vice versa. In such a situation, you have neither advantage nor disadvantage.

There is no special exception for advantage that comes from inspiration. It uses the same wording as many other features that grant advantage, without providing any extra rules.