America's billionaires have had a great year from a financial standpoint. The top 20 people on Forbes' 2023 richest list have added $310 billion to their fortunes. Together, they have a combined wealth of $1.9 trillion, a 30% increase from a year ago. To give a sense of how significant their growth is, these 20 people now hold 40% of the total wealth of the entire Forbes 400 list. Among the top 20, Nvidia Corp. CEO Jensen Huang stands out. His company, which has made big strides in artificial in