An apparatus of coupled inductors includes a first coil and a second coil arranged in a way that an inter-coil capacitance between the first coil and the second coil can keep electromotive forces induced by a first inductance of the first coil and a second inductance of the second coil about the same. As the current bypasses an unbalanced parasitic capacitor, a compensation capacitor disposed between the two coils can compensate the inter-coil capacitance of the parasitic capacitor. The apparatus of coupled inductors implemented with a specific coil arrangement or disposed with the compensation capacitor can keep the EMFs induced over the two inductances equal in amplitude, which prevents both the differential-mode and common-mode interference from being converted, improving the characteristics of mode conversion and is suitable to be utilized in a PoE system or the like.