The little hydrogen fuel cell maker still has a lot to prove.Plug Power (PLUG 1.26%), a developer of hydrogen fuel cell systems, was one of the biggest boom and bust stories of the dot-com bubble more than two decades ago. The company went public at a reverse split-adjusted price of $150 per share on Oct. 29, 1999, and its stock soared nearly tenfold to its record high of $1,498 on Mar. 10, 2000.But today, Plug's stock trades at about $2 a share. A $10,000 investment in its IPO would only be worth $160 toda ...