Switching power supply ripple hobby: when it matters

The scope is already on the output, and the trace is a thick band rather than a hairline. Switching power supply ripple hobby work usually starts there: a compact bench unit from the £40 to £60 shelf, a display that says 12.00 V, and tens or low hundreds of millivolts moving on top of that rail. The useful question is whether this circuit can live with that residue.

This page is from the Products Compared editorial team. We compared amazon.co.uk listings and UK review comments for the supplies in our laboratory power supply comparison. We did not connect a scope to these units, and we did not lab-test ripple. The millivolt figures below are single-owner measurements, as of 16 October 2026. A qualifying purchase through our links can earn a commission at no extra cost to you. A quieter class is on linear versus switching.

In short

Owner traces on two cheap 10 A switchers sit around 80 to 200 mV peak-to-peak, depending on the load. A 5 V logic board or a relay often tolerates about 100 mV of that residue. An audio stage, a radio front end or a sensor you are reading in millivolts can treat it as the signal. A ferrite can soften some content near 40 kHz. It does not make a 1 mV instrument, and the figures stay peak-to-peak.

What those millivolts are

Ripple here is the leftover movement on a DC rail. A linear bench supply rectifies the mains and regulates with a series element. A switch-mode supply chops at a high frequency so the magnetics shrink, which is why the compact boxes in this set weigh about 1.1 to 1.5 kg. Keysight's bench note puts the choice that way: match the noise and the size to the device. Under about £80, the units in this comparison are that switch-mode class.

Your scope reading is peak-to-peak. Root-mean-square is the figure a maker uses in a noise specification. GPS LTD describes its own linear range at about 1 mV rms, and that range is not in this comparison. An 80 mV peak-to-peak owner trace and 1 mV rms do not form a ratio you can quote, because these switching traces are not a clean sine. Two owners, on two models, place the £50 switchers outside a published millivolt class.

How the trace changes with the load

The same supply does not show one millivolt figure at every current. On the Wanptek 30 V 10 A, listed at £50.92 with 4.5 stars from 379 reviews, a UK reviewer measured about 100 mV peak-to-peak at 7 A, and less at a lighter load. A trace taken with the output open does not reproduce that 7 A figure.

On the Nankadf WPS3010H, listed at £59.99 with 4.4 stars from 1,517 reviews, one UK review cites about 200 mV peak-to-peak near 40 kHz, and another about 80 mV peak-to-peak at 24 V and 300 mA. They were taken at different points, and neither is a datasheet. Write the voltage, the current and how you probed it next to the millivolts.

The 5 A Nankadf is a different model. The 80 mV and 200 mV comments belong to the 10 A WPS3010H, not the WPS305H. The Jesverty SPS-3010V title says switching, and this set has no owner ripple figure for it. One owner said it was quiet on amateur radio, which is a listening impression, not a missing trace filled in.

Circuits that cope and circuits that do not

A circuit copes when the residue is small beside the thing it is trying to see. A 5 V Arduino, a logic board or a relay rarely notices about 100 mV of switching residue. That is a rule of thumb for ordinary digital work under 30 V. If the sketch is timing an analogue pin, you have already left the rule of thumb.

Audio preamps, radio front ends and sensors you read in tens of millivolts can treat the residue as the signal. A microphone or a radio mixer on that same rail sets the limit. If a receiver is already unhappy, change one thing at a time: aerial, earth, lead dress, then the supply.

What not to do with a ferrite

A ferrite on the output lead shows up in one Nankadf review, and the effect is narrow. It can take the edge off some content near 40 kHz. It does not move an 80 mV peak-to-peak rail into the 1 mV rms class GPS LTD describes for its own linear range. A band that is still the size of the signal you care about means the supply is still a switcher.

That comment does not contain a core, a turn count or a capacitor you can copy. A large electrolytic added because a forum recommended it can surge at switch-on, or ring when the load steps. If the circuit needs a filter, take the values from its own datasheet, or buy a supply whose maker published the noise with a method.

Check the probe before you blame the box. The Institution of Electronics notes that leads pick up noise. A long ground clip is a loop. Use a short ground at the terminals, keep the output leads short, and see whether the band changes at the current you actually use.

When the trace is the supply

If the band stays with short leads, a short ground and the same load, treat it as residue on the rail. Compare it with the owner figures above. Your unit can differ. A band far larger than those comments is when you look for a fault in the unit.

When to change the supply

Change the supply when the circuit needs a stated millivolt noise figure and the listing does not give one. In this amazon.co.uk set that means leaving the £50 switching band. GPS LTD's about 1 mV rms marks that other class, on products this comparison does not include. A heavier box, on its own, is not that specification.

The StonyLab 30 V 5 A, at £299, looks like the way out because the bullets say linear. This set has no review line and no ripple figure, and the attribute table contradicts itself, including a maximum written as 30 V AC rather than a UK mains rating. Skip it until a figure and a review exist.

More voltage is the other false exit. The RUZIZAO that goes up to 400 V also says switching, at £319.96, and that range is a shock hazard on a 12 V hobby rail. BS EN 61010-1 covers shock from live terminals when the output is on. Extra volts do not cancel residue. Stay under 30 V unless you already work at the higher voltage.

For digital work under 30 V, a switcher from this band is the ordinary buy once the watt ceiling and the plug match the job. The Jesverty SPS-3010V is the top pick for a general 30 V bench that may want 10 A, after you confirm the mains selector: the bullets say 115/230 V selectable and the table says 115 V. Skip it for a quiet linear rail or a second output. The Nankadf WPS305H, at £49.99 with 4.5 stars from 1,045 reviews, is the best value inside 0–30 V and 0–5 A. Volts, amps and the BS 1363 lead are on the bench power supply buying guide. The current limit on a board is on bench power supply for electronics repair.

A return is separate from a topology limit. The Consumer Rights Act 2015 expects goods from a trader to be of satisfactory quality and as described. Damage, a rail that will not hold the voltage you set, or a plug that is not a sound BS 1363 fitting belongs with the seller. A return is a weak complaint when the title says switching and no millivolt figure was promised.