In a large bowl, marinate corned beef with maple syrup, mustard, garlic powder, salt, pepper, and marjoram for 15 minutes or up to 2 hours. *Discard any spice packets the corned beef comes with.*
Pour 4 cups of beef broth into the bottom of the Instant Pot.
Using an insert or basket for the Instant Pot, add in the corned beef and set to high pressure for 90 minutes. Once the timer is up, press cancel and allow for a natural release.
Once the Instant Pot has depressurized, remove corned beef to a casserole dish and cover to allow to rest.
Drain the Instant Pot.
Put a basket in the IP with the carrots, cabbage and water. Cover the IP and cook for 4-5 minutes on high pressure.
Serve corned beef alongside the cabbage and carrots.