You may have baked with "Marmoset" tangent space, which can be seen from the bake settings. It's unique to Marmoset itself, and is not synced with other rendering engines. Set it to Mikk / xNormal, which is supported by Substance Painter and many other real-time game engines. I also assume your low poly is triangulated…
Would you be able to elaborate why triangulating a mesh before baking would yield a better result? I too had just started using Marmoset and this had caught my eye.