Deep-sea exploration serves as a core technical field for marine resource prospecting, geoscientific research, marine ecological monitoring, underwater archaeology, deep-sea rescue and national defense security. The deep-sea environment features extreme characteristics such as ultra-high hydrostatic pressure, strong seawater corrosion, low light, high humidity, intense electromagnetic shielding, long-distance signal transmission and unmanned operation. Hydrostatic pressure increases by one atmosphere for every 10 meters of water depth, exceeding 100 MPa in the Mariana Trench at full ocean depth. High-voltage power supplies are critical components for deep-sea equipment, delivering stable high-voltage bias, power driving, sonar emission and signal amplification for side-scan sonars, multi-beam bathymetric systems, underwater synthetic aperture radars, in-situ chemical analyzers, ROVs/AUVs, deep-sea landers, underwater gliders, ocean-bottom seismometers and underwater laser radars. They convert power from subsea batteries or umbilical cables into high-voltage power for subsea systems. Their sealing reliability under extreme pressure, corrosion resistance, underwater insulation stability, long-term operational robustness and environmental adaptability directly determine diving depth, continuous operating time, detection accuracy and overall mission success. Deep-sea applications impose extreme requirements far beyond conventional industrial power supplies. First, sealing and structural reliability under ultra-high hydrostatic pressure. Deep-sea equipment operates from hundreds to tens of thousands of meters, enduring pressures above 100 MPa at full ocean depth. Conventional seals fail, housings deform and water ingress occurs under such pressure; internal high-voltage insulation also degrades severely, risking breakdown and short circuits. Power supplies must withstand up to 120 MPa with permanent watertight integrity and stable internal insulation under extreme pressure. Second, long-term protection against severe seawater corrosion. Seawater is a highly conductive electrolyte rich in chloride ions, salts and microorganisms, causing aggressive corrosion and biological fouling that degrade metals, electronics and insulation while damaging seals. Subsea systems often remain deployed for months or years without maintenance, requiring exceptional corrosion and fouling resistance with no permanent degradation during prolonged immersion. Third, underwater high-voltage insulation and ultra-low electromagnetic interference. High seawater conductivity creates intense electric fields around high-voltage outputs, triggering leakage, arcing and electrochemical erosion. Meanwhile, high-precision sonar and sensing systems are highly sensitive to switching noise and electromagnetic radiation coupled through seawater and umbilical cables, distorting detection signals. Designs must limit leakage current below 10 μA while maintaining minimal conducted and radiated interference. Fourth, miniaturization, lightweight design and high power density. ROVs, AUVs and gliders face strict volume, weight and buoyancy constraints. Traditional oil-filled power units are bulky and heavy; modern systems require extreme compactness and high power density optimized for buoyancy balance. Fifth, long-distance underwater power transmission optimization. Deep-sea observatories and remote ROVs rely on multi-kilometer umbilical cables with significant impedance, parasitic capacitance and inductance, causing severe voltage drop, power loss, signal attenuation and coupling interference. Power supplies must stabilize output under long cable feed and support integrated power-and-signal transmission over the same umbilical line. Sixth, high reliability and redundancy. Unplanned shutdowns lead to mission failure or equipment loss with massive economic impact. Systems require MTBF ≥ 1×10⁵ hours, design life ≥ 10 years, full redundancy and automatic fault recovery. Seventh, wide input voltage range and high efficiency. Battery-powered and long-cable-fed systems experience large voltage fluctuations during discharge and varying loads. Input must cover 50%–150% of nominal voltage with overall conversion efficiency ≥ 92% to extend endurance and reduce cable losses. Eighth, comprehensive protection and underwater environmental adaptability. Power units must handle short circuits, open circuits, surges and temperature variations while operating stably from 0 ℃ to +60 ℃ seawater with full overvoltage, undervoltage, overcurrent, short-circuit, overtemperature, leakage and arc protection. This methodology establishes a complete technical framework covering full-ocean-depth pressure-resistant sealing, watertight protection, seawater corrosion defense, underwater high-voltage insulation, long-distance transmission adaptation and deep-sea reliability engineering. It provides standardized design guidelines for localized high-performance deep-sea power supplies. Addressing core challenges including ultra-high pressure sealing, severe corrosion, underwater insulation limits and long cable feed, the universal architecture adopts fully sealed oil-filled modular isolation topology + pressure compensation system + fully digital closed-loop control, reinforced with integrated corrosion protection and optimized underwater insulation. This overcomes traditional weaknesses such as poor sealing, corrosion vulnerability, insufficient insulation and excessive weight. Eight core design principles are defined: 1. Full-ocean-depth pressure housing and redundant sealing. Housings use high-strength titanium alloy, duplex stainless steel or carbon-fiber composites; titanium alloy is preferred for full ocean depth due to superior specific strength and corrosion resistance. Integrated forging or spin forming minimizes welds. Finite element optimization ensures controlled deformation without plastic failure at 120 MPa. Sealing adopts multi-stage redundant metal face seals combined with fluororubber or perfluoroelastomer O-rings with low permanent compression set. Dual or triple independent sealing stages include leakage monitoring ports for early failure warning. Deep-sea dedicated watertight connectors match full depth ratings with redundant interface sealing. 2. Pressure compensation system design. Passive piston or bladder compensators connect internally to insulating oil chambers, exposing external surfaces to seawater to balance internal oil pressure slightly above ambient seawater pressure. This eliminates unidirectional housing stress and compensates oil volume changes caused by temperature and depth, preventing negative-pressure water ingress. Compensation volume covers full temperature and depth ranges with stroke monitoring for oil leakage alarms. Ultra-deep systems adopt active hydraulic compensation with pressure sensors and micro pumps for dynamic pressure balance. 3. Insulating oil selection and internal insulation optimization. High dielectric-strength low-viscosity synthetic insulating oil provides ≥50 kV/2.5 mm breakdown performance, excellent thermal conductivity and long-term chemical stability. Internal high-voltage components such as transformers and rectifiers implement field grading structures to eliminate localized high stress and partial discharge. High-voltage windings use oil-resistant polyimide multi-layer insulation; creepage distances are enlarged with anti-surface-flash structures. PCBs undergo conformal coating and potting to resist oil contaminants and moisture. 4. Modular isolated power conversion topology. A three-stage architecture applies: front-end APFC achieves power factor >0.99 to reduce harmonic loss for long umbilical feed; intermediate full-bridge LLC resonant isolation realizes ZVS primary and ZCS secondary soft switching across wide voltage and load ranges for ultra-low noise and high efficiency; rear high-voltage symmetric voltage-doubler rectification reduces transformer stress and simplifies insulation. Optimized resonance maintains soft switching universally with peak efficiency ≥92%. Dual galvanic isolation provides insulation withstand ≥ twice maximum output voltage for subsea safety. 5. Four-level seawater corrosion protection. Material selection uses titanium alloy, duplex stainless steel or Hastelloy for wetted parts; non-metallic components adopt PTFE, perfluoroelastomer and UHMW-PE. Surface treatment includes anodization, passivation and pinhole-free fluoropolymer coatings. Cathodic protection integrates zinc or aluminum sacrificial anodes. Structural design eliminates stagnant gaps; welds are smoothed; vulnerable connectors are replaceable with anti-scour shielding. 6. Underwater low-noise electromagnetic compatibility. LLC soft switching reduces dv/dt and di/dt at the source. Multi-layer shielding includes internal metal shielding cavities plus conductive pressure housings achieving shielding effectiveness ≥60 dB against seawater coupling. Multi-stage EMI filtering suppresses conducted interference; high-voltage outputs apply π-filter networks limiting ripple below 0.1% peak-to-peak. Umbilical interfaces implement impedance matching to mitigate reflection. Strict single-point grounding separates power, analog, digital and shield grounds to eliminate ground-loop noise. 7. Miniaturization and high integration. Higher switching frequency (100 kHz–200 kHz) reduces magnetic component size. Highly integrated power modules and 3D stacked layouts improve space utilization, achieving power density ≥200 W/in³. Lightweight optimized housings balance mechanical strength with buoyancy requirements for AUV/ROV payload constraints. 8. Long-distance subsea transmission optimization. Shore-side high-voltage DC transmission reduces cable current and drop; subsea units locally convert to required high voltage. Impedance matching and reactive compensation suppress umbilical resonance caused by parasitic capacitance and inductance. Power-line carrier (PLC) enables combined power-and-signal communication over a single cable, simplifying umbilical architecture. Long-term full-life reliability is ensured through comprehensive redundancy, advanced thermal management, environmental hardening and intelligent health monitoring. Three-level redundancy eliminates single-point failures at component, module and system levels with seamless hot swap. Thermal design relies on oil conduction + housing natural convection to seawater; internal oil circulation via micro pumps improves uniformity. All electronics endure wide temperature, high humidity and salt fog; full conformal coating and potting prevent degradation. Integrated health management continuously monitors voltage, current, temperature, internal oil pressure, seal status and compensator stroke, transmitting diagnostics topside with predictive failure alerts. Automatic recovery handles transient faults with watchdog reset for controller stability. Full safety protection includes comprehensive hardware-fast (<1 μs) dual overvoltage, overcurrent, short-circuit, overtemperature, leakage and arc detection. Subsea interlocks trigger safe shutdown during flooding or attitude anomalies; remote emergency power cut is available topside or via acoustic commands. Redundant emergency batteries maintain critical communication for vehicle recovery; fast high-voltage residual charge bleeding ensures personnel safety during retrieval and maintenance. This methodology fundamentally solves traditional deep-sea power supply limitations regarding extreme-pressure sealing failure, corrosion aging, insufficient underwater insulation and excessive weight. Multi-redundant sealing plus pressure compensation enables reliable full-ocean-depth operation up to 120 MPa; graded corrosion protection ensures service life beyond 10 years; oil-filled optimized insulation stabilizes high-voltage performance underwater; LLC soft-switch topology delivers ≥92% efficiency with ultra-low interference compatible with high-precision detection systems. Widely applicable to ROVs/AUVs, landers, gliders, seabed observatories and resource exploration equipment, it provides core technical support for domestic substitution and full-ocean-depth performance breakthroughs in China’s deep-sea exploration industry.