"Pennsylvania is at an energy crossroads,” PUC Chairman Steve DeFrank said in a statement. “Data center development brings significant opportunities, but that growth cannot come at the expense of the families and businesses that already depend on reliable and affordable electric service.”

Stephen M. DeFrank is a Democrat, based on his documented political/career history.

The Pennsylvania Manual identifies DeFrank as having previously served as:

Chief of Staff to State Sen. Lisa Boscola (D)
Executive Director of the Democratic Consumer Protection & Professional Licensure Committee
Executive Director of the Democratic Policy Committee
Special Assistant to the Democratic Leader
Chief of Staff to State Sen. Richard Kasunic

The Pittsburgh Post-Gazette likewise described him in 2022 as Boscola's former chief of staff when reporting on his appointment to the PUC.

He was appointed to the PUC by Gov. Tom Wolf in 2022 and subsequently named PUC Chairman by Democratic Gov. Josh Shapiro in August 2023.

So, while PUC commissioners are appointed regulators rather than elected legislators, DeFrank's political affiliation/background is Democratic.