eTopxizu (cheapowatt) 30 amp power supply Guinea Pig

The "blue thingy" is metalisized polypropelyne capacitor, highly unlikely that was the cause of any sound. Adjacent to it is an inductor with adhesive and three circuit trace connectors, more of a likely canidate for buzzing than the cap.

When ordering the replacement FET, the package size (220), the lead spacing, and base=collector-emitter locations are the next most important besides the electrical characteristics. Just order the Fairchild part with similar numbers that replaces your original.