This little hydrogen energy company still has a lot to prove.Plug Power (PLUG 6.87%) was one of the hottest stocks of the dot-com bubble. The provider of hydrogen charging solutions went public at a reverse split-adjusted price of $150 in October 1999 and hit a record high of $1,498 on March 10, 2000.But today, Plug Power's stock trades at less than $3. Its investors retreated as the dot-com bubble burst, its growth slowed down, and it racked up steep losses. A delayed filing of its annual report for 2020 - ...