How to use a bench power supply
Updated: October 2026
The supply is already on the bench and the current limit is still at maximum from yesterday. That is how a small board gets damaged. How to use a bench power supply is an order: output off, set the voltage, set a limit you can justify, connect plus and minus, then enable and read the lamp. Examples come from our [laboratory power supply comparison](/hub/workshop/laboratory-power-supply). Products Compared did not lab-test these units. Listing notes are as of October 2026. A qualifying purchase can earn a commission at no extra cost to you.
The supply is already on the bench and the current limit is still at maximum from yesterday. That is how a small board gets damaged.
The supply is already on the bench and the current limit is still at maximum from yesterday. That is how a small board gets damaged. How to use a bench power supply is an order: output off, set the voltage, set a limit you can justify, connect plus and minus, then enable and read the lamp. Examples come from our laboratory power supply comparison. Products Compared did not lab-test these units. Listing notes are as of October 2026. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Output switch | Current limit | USB charge port | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Jesverty Jesverty SPS-3010V | Yes, unless OPN is enabled | Adjustable, OCP claimed | USB-A and USB-C, 20 W claimed | 8.6 | about £50.99 | View offer |
| Best value |  NANKADF NANKADF WPS305H | Yes | Adjustable, OCP alarm on a long press | USB, 18 W claimed | 8.2 | about £49.99 | View offer |
| Alternative |  WANPTEK WANPTEK 30 V 10 A | n/a | Adjustable to 10 A, OCP claimed | USB-A and USB-C | 7.8 | about £50.92 | View offer |
On this page
Set it before anything is connected
Keep the output off while you set the numbers. Electronics Info Line calls the limit the safety control: set voltage and current with nothing connected, then enable. A tutorial uses about one and a half times the current you expect. If you do not know the current, start far below the supply’s maximum. Leaving the knob at 10 A because the title says 10 A offers a small track far more current than it can survive. Set the voltage the circuit actually wants. Plus goes to the circuit positive and minus to the circuit negative. The green or centre terminal on several units here is mains earth, not a spare negative. Check the BS 1363 plug before the first enable.
Enable and read the lamp
Clip plus and minus only after the numbers are set, then enable. If there is no output button, mains-on is the enable, so the board stays disconnected until voltage and limit are already right. Read the lamp next. CV, constant voltage, means the supply is holding the voltage you asked for and the load is under the limit. CC, constant current, means the limit is active and the voltage falls. The Institution of Electronics states that mode depends on the settings and the load. Switch off and look for a short, a reversed module, or a limit left in the wrong units. Turning the knob up to clear the lamp throws away the protection. CC then CV is not a lithium-ion charge profile.
Traps on the supplies in this set
There is no single button sequence for every listing. On the Nankadf WPS305H and WPS3010H the OUTPUT button is the enable. The WPS305H listing ties a long press to the over-current alarm, so use the manual. Weak crocodile clips are a repeated complaint on the 5 A Nankadf. A clip that slips off mid-test looks like a dead rail. On the Jesverty SPS-3010V, OPN changes the order. Enabled, the listing says the output comes on with the mains switch. Disabled, you use the OUTPUT button. USB, about 20 W claimed on the Jesverty and about 18 W on the Nankadf units, is not the variable rail. The RUZIZAO SPS-E3010 fan runs from switch-on, which is idle noise, not a CC fault.
When to stop
Stop when the problem is no longer a knob. A cracked plug, a wrong fuse or a hot case at idle means the output off and the mains unplugged. Do not open the case. If you employ people, the Electricity at Work Regulations 1989 apply at work. HSE does not demand a yearly PAT test in every case, and that is not a reason to ignore a burning smell. The RUZIZAO R-SPS4001S lists 0–400 V, and a current limit does not make that a beginner rail. Get help for fixed wiring and for a calibration other people will trust. If the supply behaves and the board does not, use the bench power supply for electronics repair page.
Common questions
In what order do I set voltage and current?
With the output off and the board disconnected, set the voltage, then a current limit near the draw you expect. About one and a half times that draw is only a tutorial rule of thumb. Connect plus and minus, then enable. Follow your own manual if it gives another order. Do not short the terminals because a different brand tells its owners to.
What does the CC lamp mean?
Constant current. The load wants more than your limit, so the voltage falls. A healthy board on a sensible limit should show CV instead. Switch off and check the board or the setting. CC is not, on its own, a failed power supply. The Institution of Electronics treats the mode as the joint result of the settings and the load.
Do I connect to the green earth terminal?
Not as the circuit negative. A Jesverty review says the centre post is mains earth and there is still only one output. Use plus and minus for the rail. Use earth only when the setup truly needs a chassis bond. Parking a ground on the green socket because it is spare creates a path you did not plan.
Should the output be off while I clip on?
Yes. Set the numbers, attach plus and minus with the output disabled, then enable and watch the lamp. The Nankadf OUTPUT button is that control. On the Jesverty it is the same unless OPN is on, in which case the rail follows the mains switch. Where no output switch is described, keep the board off until the settings are already correct.
What is OPN on the Jesverty?
OPN applies the Jesverty output as soon as you switch the supply on. With OPN off, the OUTPUT button keeps the terminals dead while you set voltage and current. Check the mode before the clips touch a board. If you expected a separate enable and OPN is on, the leads can be live sooner than you think.
Can I use the USB port to power the board?
Not when you need the current limit you set. USB here is a charger or a data port, and a Wanptek review says that current is fixed. Claims around 18 W or 20 W are phone-charger class, not the 0–30 V terminals. Power the board from plus and minus so the limit you set is the one the board sees.
When do I stop and get help?
Stop for a damaged plug or lead, a hot smell, current limit with nothing attached, 400 V work, fixed wiring, or a calibration someone else will rely on. Do not open the case. Working alone does not create an employer’s duty, and it does not make a live chassis a reasonable experiment.
Related pages
Sources
Public UK sources used for this comparison, retrieved in October 2026. Listing prices, stars, and review counts are the amazon.co.uk lines in this set.
- Electrical Equipment (Safety) Regulations 2016 (retrieved October 2026)
- BS EN 61010-1:2010+A1:2019 (retrieved October 2026)
- HSE, frequently asked questions on portable appliance testing (retrieved October 2026)
- HSE INDG236, maintaining portable electric equipment (retrieved October 2026)
- Electrical Safety First, plugs and fuses (retrieved October 2026)
- Keysight, linear versus switching power supplies (retrieved October 2026)
- Electricity Safety, Quality and Continuity Regulations 2002 (retrieved October 2026)
- Institution of Electronics, constant voltage and constant current (retrieved October 2026)