A ceramic capacitor with the designation CAP CER 3900PF 1.2KV X7R 1808 has a capacitance of 3900 pF ±20 and can withstand a voltage of up to 1200V (1.2kV). It is classified as an X7R material, which means it has a relatively stable dielectric constant over temperature variations. This capacitor has a metric size designation of 1808.