DC-link capacitor selection depends on several key parameters: required capacitance for voltage regulation, ripple current capability for your switching frequency and power level, voltage rating with appropriate derating (typically 80-90% of bus voltage), and temperature requirements for your application. For switching power supplies with significant ripple current, consider a hybrid approach using both film capacitors (for high-frequency ripple) and electrolytic capacitors (for bulk storage).

X capacitors are connected across the line (line-to-line) and are designed to fail open to prevent fire hazards. Y capacitors are connected line-to-ground and are designed to fail without creating shock hazards. X capacitors suppress differential mode noise while Y capacitors suppress common mode noise. For equipment without safety ground, use only X capacitors for EMI filtering.

The expected life follows the Arrhenius equation: L = L0 × 2^((T0-T)/10) × 2^((IR0-IR)/0.1), where L0 is rated life at reference temperature T0, T is actual operating temperature, and IR is the applied ripple current ratio. For example, a capacitor rated for 2000h at 105°C will have 16,000h life at 85°C with 50% of rated ripple current.

Key factors include: required impedance at frequencies of concern (typically 150kHz to 30MHz), current rating with appropriate derating (allow 20-50% margin), DC bias effects on inductance, physical size constraints, and temperature range requirements. For power line applications, consider saturation effects from DC bias current. For signal line applications, focus on high-frequency performance with minimal insertion loss.