Fossil fuel plants are chemical -> heat -> mechanical -> electrical. The heat -> mechanical step is the inefficient one, sadly limited to ~40% efficiency even with very fancy machinery. Most other conversions can be above 90% efficient.
The efficiency of gas-fired combined cycle power plants can exceed 60% (lower heating value). And their capex is just over $1/W. Combustion turbines are amazing.
With a SOFC topping cycle they might approach 70-80% efficiency. SOFC with just a combustion turbine (no steam bottoming) could exceed 60%. Granted, SOFCs are direct chemical->electrical conversion, but their waste heat is very usefully hot.
I don't think it's entirely a coincidence that nuclear power plants in the US stopped being built about the same time combustion turbines (by themselves, without the steam bottoming cycle) reached efficiency parity with high temperature steam turbines.
(SOFC = solid oxide fuel cell, which operate around 1000 C.)
("Lower heating value" is based on energy that could be obtained burning natural gas to CO2 and water vapor. An additional 10% could be obtained by condensing the water vapor to liquid, this is "higher heating value".)
