Plug Power (PLUG 1.12%) stock rocketed more than 10% in early trading Tuesday, hitting $3 per share before giving back most of its gains and retreating to a single-digit gain. As of 10:20 a.m. ET, Plug stock is still up, but only by 2%.So why did Plug Power go up in the first place, and why did it give up its gains so quickly?Plug Power's good news TuesdayIn a note out this morning, investment bank Morgan Stanley predicted Plug Power will receive Department of Energy approval for a $1.7 billion loan by the ...