Here in this category there are a few things that may not be noticed if looking at it on a year-by-year basis. Namely not only are there two two-time winners (Osment and Robbins) but also four cross-over winners (Meaning they won both Lead and Supporting prizes).

Without much further ado The Best Supporting Actor Winners:

2020 Dean-Charles Chapman 1917

2019 Samuel L. Jackson Captain Marvel 

2018 Michael B. Jordan Black Panther

2017 Sam Rockwell Three Billboards Outside Ebbing, Missouri

2016 Daniel Fripan Der Bunker

2015 Sonny Young Still

2014 Robert Duvall The Judge

2013 Ben Kingsley Iron Man 3

2012 Leonardo DiCaprio Django Unchained

2011 Alan Rickman Harry Potter and the Deathly Hallows, Part 2

2010 Will Poulter The Chronicles of Narnia: The Voyage of the Dawn Treader

2009 Christoph Waltz Inglourious Basterds

2008 Robert Downey, Jr. Tropic Thunder

2007 Jack Nicholson The Departed

2006 Gabriel Byrne Wah-Wah

2005 Erland Josephson Saraband

2004 Rodrigo Santoro Carandiru

2003 Tim Robbins Mystic River

2002 Haley Joel Osment Edges of the Lord

2001 Jude Law Artificial Intelligence: A.I.

2000 Haley Joel Osment Pay it Forward

1999 Tim Robbins Arlington Road

1998 Nick Nolte U Turn

1997 Lucas Black Sling Blade

1996 Chazz Palminteri Mulholland Falls