Answer:
According to exit polls from presidential elections, in the five elections between 1992 and 2008, on average 88% of African-Americans voted for the democratic candidate, while slightly over 9% voted for the republican candidate. The rest voted for a third-party candidate.
The 2008 election, which featured Barack Obama seeking to become the first African-American president, saw a significant increase in the percentage of African-Americans voting for the democratic candidate, with most exit polls putting the percentage somewhere between 95% and 98%.