What Are Switch Mode Power Supplies?

Switch mode power supplies convert AC mains voltage to regulated DC output by rapidly switching transistors on and off — typically at frequencies between 50kHz and 500kHz. That's the short version. The longer explanation involves high-frequency transformers, pulse-width modulation, and feedback loops, but honestly, what matters to most of us is the end result: a lighter, more efficient, and cooler-running power supply than the old linear designs.

I've been using bench PSUs for years — started with a heavy old linear unit that weighed about as much as a bag of cement. Brilliant build quality, sure, but try lugging that to a portable setup or fitting it on a crowded workbench. When I switched to a modern switching mode power supply, the difference was immediate. Half the weight. Same output. Less heat pouring off the back.

The basic principle hasn't changed much since the 1970s, but the components have. Modern MOSFETs, better capacitors, and smarter control ICs mean today's switching PSUs are quieter, more stable, and far more reliable than the early designs that gave SMPS a bad reputation among radio enthusiasts. (If you used one of those early units, you'll know exactly what I mean — they were genuinely awful.)

Switch Mode Power Supplies vs Linear: The Real Differences

This is where the debate gets heated — especially in ham radio circles. Linear power supplies regulate voltage by dissipating excess energy as heat through a series pass transistor. Simple, effective, and inherently low-noise. But that simplicity comes at a cost: massive transformers, poor efficiency, and serious weight.

Switching power supplies do the same job differently. They chop the input voltage at high frequency, step it down through a small transformer, then smooth and regulate the output. The result? Less wasted energy, smaller components, and dramatically reduced weight.

So what's the catch?

Noise. That high-frequency switching generates electromagnetic interference. For someone running a bench light or charging batteries, it's irrelevant. For a ham radio operator trying to pull weak signals out of the HF bands? It can be a real problem. Well, actually — it used to be a real problem. Modern designs have largely sorted this, which I'll cover in the noise section below., a favourite among Britain’s tradespeople

For a deeper technical breakdown, I've written a separate piece on SMPS vs linear PSU performance for radio use that goes into oscilloscope measurements and real-world testing.

Why 13.8V 30A Is the Standard for Ham Radio Power Supplies

The 13.8V figure isn't arbitrary. It matches the nominal voltage of a fully charged 12V lead-acid battery under float charge — which is exactly what most mobile radio equipment was originally designed to run from. Every major transceiver manufacturer (Icom, Yaesu, Kenwood) specs their base station radios for 13.8V DC nominal input.

The 30A rating gives headroom. A 100W HF transceiver draws roughly 20–22A on transmit. You want at least 25% headroom above peak draw to avoid voltage sag and to keep the PSU running within its comfort zone. A 13.8V 30A bench power supply handles this perfectly.

Regulated Output: Why ±0.1V Matters

A properly regulated 13.8V DC power supply for radio holds output within ±0.1V from no load to full load. That stability matters because transceivers can behave unpredictably with voltage fluctuations — reduced output power, distorted audio, or even protection circuit trips. I've seen a mate's rig shut down mid-QSO because his cheap unregulated supply sagged to 11.9V under key-down.

The best bench PSU 13.8V 30A units available in the UK this spring maintain regulation within ±0.05V, which is spot on for demanding applications. Look for units with both voltage and current metering on the front panel — you'll want to see exactly what's happening during transmit.

Noise, Interference, and the Low Noise Switching Power Supply Revolution

Here's where things have genuinely changed. Five years ago, I'd have told anyone running HF to stick with linear. Not anymore.

Modern low noise switching power supply designs incorporate what manufacturers call Noise Offset Control (NOC). This clever bit of engineering shifts the switching frequency and its harmonics away from the amateur bands you're actually using. The result? Noise floors comparable to linear supplies on the bands that matter to you.

I tested a ham radio power supply 13.8V unit with NOC against my old linear supply on 40m and 20m. Honestly? I couldn't tell the difference on the waterfall display. The noise floor was within 1–2dB. That's remarkable for a unit weighing under 2kg.

That said, not all switching supplies are equal. Budget units without proper filtering or shielding can still spray interference across the HF spectrum. If you're buying a bench power supply for ham radio UK, check specifically for:

• NOC or equivalent frequency-shifting technology
• Internal EMI filtering on both input and output
• Shielded enclosure with proper grounding points
• CE and UKCA marking — these confirm EMC compliance per UK electromagnetic compatibility regulations

For more on choosing between compact and linear units specifically for amateur radio, see our compact vs linear PSU comparison for ham operators.

Buying Guide: Switch Mode Power Supplies for the UK Market in 2026

Right, let's get practical. What should you actually look for when buying a DC bench power supply UK in 2026? I've narrowed it down to the factors that genuinely matter — not marketing fluff.

Output Voltage and Current

For ham radio: 13.8V 30A is the sweet spot. For general bench work, a variable output (0–30V, 0–10A) gives more flexibility but won't handle high-current radio work. Know your primary use case before buying.

Protection Features

Non-negotiable. Every decent 13.8V regulated power supply UK should include:

• Over-voltage protection (OVP) — typically trips at 15.5–16V
• Over-current protection (OCP) — foldback or hiccup mode
• Short-circuit protection — must be automatic recovery
• Over-temperature protection — shuts down before damage occurs

These aren't optional extras. They protect both your supply and whatever expensive equipment sits downstream. The HSE electrical safety guidance is worth reviewing if you're setting up a workshop environment.

Build Quality and Compliance

Look for UKCA marking (mandatory for the UK market since 2025), CE marking if buying from EU suppliers, and ideally compliance with BS EN 61558 safety standards for transformers and power supplies. Cheap imports without proper certification aren't worth the risk — I've seen one melt a connector because the terminal ratings were wildly optimistic., popular across England

Cooling and Noise

Fan noise matters if you're operating in a home shack. The best units use temperature-controlled fans that stay silent at low loads and only spin up under heavy draw. Some premium models quote fan noise under 30dB at 50% load — that's quieter than a library.

Connectivity

A 13.8V 30A bench power supply UK should offer heavy-duty binding posts (rated 30A minimum), Anderson Powerpole compatibility, and ideally a front-panel cigarette lighter socket (10A rated) for handheld radios and accessories. Multiple output terminals let you run several devices simultaneously without daisy-chaining.

Worth the extra spend? Absolutely. A proper 30 amp 13.8 volt DC power supply UK with decent terminals saves hours of faffing with adapters and reduces voltage drop at the connections.

Browse the full range of tested units at jaogaubench.co.uk, where we stock models specifically selected for the UK amateur and professional market.

Key Applications Beyond Radio

Ham radio drives most 13.8V 30A power supply for ham radio searches, but these units serve far broader purposes. I use mine daily for tasks that have nothing to do with RF.

Automotive Electronics Testing

Testing car stereos, amplifiers, LED lighting, and ECU modules on the bench. A stable 13.8V supply simulates a running vehicle's electrical system perfectly. I've diagnosed more car electrical faults on my bench than under a bonnet — much easier when you can control the supply voltage precisely.

CCTV and Security Systems

Powering 12V camera systems during installation and testing. A 30A switch mode power supply 13.8V can run an entire multi-camera system simultaneously for commissioning checks.

RC and Drone Charging

High-current chargers for LiPo batteries need a solid DC source. A 30A supply handles even 6S charging at high rates without breaking a sweat., with availability in Scotland

LED Lighting Projects

12V LED strips, architectural lighting prototypes, and signage testing. The regulated output prevents colour temperature shifts that occur with voltage variation.

For those needing an AC to DC converter at 13.8V for UK mains, we've put together a dedicated guide covering input voltage considerations for 230V 50Hz supply.

Key Takeaways

• Weight advantage: Switch mode power supplies weigh 1.5–2.5kg versus 8–12kg for equivalent linear units — a 75–80% reduction.
• Efficiency: SMPS delivers 85–92% efficiency compared to 40–55% for linear, meaning less heat and lower electricity costs over time.
• Noise is solved: Modern NOC technology reduces RF interference by 20–40dB, making switching supplies viable for HF ham radio in 2026.
• Price point: A quality 13.8V 30A bench power supply UK costs £55–£130 — roughly half the price of an equivalent linear unit.
• Protection matters: Always verify OVP, OCP, short-circuit, and over-temperature protection are included. Non-negotiable for protecting downstream equipment.
• Compliance: UKCA marking and BS EN 61558 compliance confirm the unit meets UK safety and EMC requirements — don't skip this check.
• Versatility: Beyond radio, these supplies handle automotive testing, CCTV commissioning, RC charging, and LED projects with equal competence.