Clear Street just downgraded Plug Power (PLUG) to “Hold” from “Buy,” warning that the hydrogen fuel cell company's valuation has gotten stretched after a wild rally. Shares have rocketed more than 150% over the past month, crushing the Russell 2000's modest 3% gain during the same period. The investment firm set a $3.50 price target, below where the stock currently trades, around $3.90. The downgrade comes at a turbulent time for Plug Power. CEO Andy Marsh, who led the company for nearly 18 years, will st ...