Helion's unorthodox approach to fusion power and relative secrecy has earned it plenty of fans — and critics. But don’t count its investors among the naysayers.

Microsoft-backed startup now valued at $5.4B Fusion energy startup Helion has yet to prove it can generate electricity, but that hasn't stopped investors from dumping another $425 million into the venture.

Seattle-area company Helion Energy gets $425 million from investors including Sam Altman and Softbank to pursue clean energy's "Holy Grail."