6.8 µF, 25 V molded tantalum — bypass and hold-up fit
The TAJW685K025RNJ: This is a 6.8 µF, 25 V molded tantalum capacitor from the KYOCERA AVX TAJ series, in a 2312 (6032 Metric) case with size code W. The ±10% tolerance and 2 Ohm ESR are the numbers that matter for decoupling and filter applications: the ESR sets the ripple voltage at the switching frequency, and the 25 V rating gives headroom on a 12 V or 5 V rail.
At 6.8 µF and 2 Ohm ESR, the self-resonant frequency sits in the low-MHz range. For a 100 kHz buck converter, the ripple voltage at the output is roughly I_ripple × ESR — a 100 mA ripple current produces 200 mV of ripple. If that is too high, a lower-ESR tantalum or a ceramic in parallel is the fix.