**Introduction:**
Both electrochemical (galvanic) cells and electrolytic cells are devices that involve the conversion of chemical energy into electrical energy. While they have some similarities, there are also key differences between these two types of cells. In this response, we will examine the statement and determine which option is correct for both types of cells.

**Explanation:**

**(a) ΔG = -nFE:**
- This equation, known as the Gibbs free energy equation, relates the change in free energy (ΔG) to the number of moles of electrons transferred (n) and the Faraday constant (F) multiplied by the cell potential (E).
- In an electrochemical cell (galvanic cell), this equation holds true as the spontaneous redox reaction releases energy and drives the flow of electrons from the anode to the cathode.
- In an electrolytic cell, this equation is also valid, but the sign of ΔG is positive since the non-spontaneous reaction requires an input of energy.

**(b) Free energy decreases in both cells:**
- This statement is incorrect. In an electrochemical cell (galvanic cell), the free energy decreases as the reaction proceeds spontaneously, releasing energy.
- However, in an electrolytic cell, the free energy increases as energy is supplied to drive the non-spontaneous reaction.

**(c) The cell potentials are temperature independent:**
- This statement is incorrect. The cell potential (E) of an electrochemical cell is temperature dependent and can be affected by changes in temperature.
- The Nernst equation is used to calculate the cell potential at non-standard conditions, taking into account the temperature and concentrations of the species involved.
- In an electrolytic cell, the cell potential is also temperature-dependent, although the purpose of an electrolytic cell is not to generate electrical energy but rather to drive non-spontaneous reactions.

**(d) Chemical energy is converted into electrical energy in both cells:**
- This statement is correct. In both electrochemical (galvanic) cells and electrolytic cells, chemical energy is converted into electrical energy, although the processes and purposes differ.
- In an electrochemical cell, the spontaneous redox reaction releases energy, which is harnessed to drive a flow of electrons through an external circuit, generating electrical energy.
- In an electrolytic cell, an external power source is used to drive a non-spontaneous redox reaction, converting electrical energy into chemical energy.

**Conclusion:**
Among the given statements, the correct statement for both electrochemical (galvanic) cells and electrolytic cells is (d) Chemical energy is converted into electrical energy in both cells. This is true as both types of cells involve the conversion of chemical energy into electrical energy, although the processes and purposes differ.