Using a “Power Supply Tester” to test an ATX computer PSU (and a voltmeter too)

I have been building computers for almost twenty years and it seems like I’ve always got one machine in the house in some state of being “upgraded.” I came across this little gadget on Amazon and thought, “hey, that is simpler than using a multimeter.”

It came from China and it was here in literally a week. (The last few things I’ve gotten from China have been sent lightning fast.)

Anyway, so the Power Supply Tester comes with literally no instructions. This turned out to be a good thing. It makes for a good kids project to figure out: (A) how it should work, (B) whether it, in fact, works like we think it should, and (C) whether or not it is accurate.

So, we starting reading up on the ATX Power Supply specification. There is a huge amount of interesting information available regarding how the ATX standard came about, who promotes the standard, and so on.

It turns out that we have a great “demo” power supply that actually has a minor issue (over voltage) that the tester detects. We use the Power Supply Tester to check the “good power” self test result in miliseconds, and test both the 24 pin motherboard connector as well as a 6 pin, twelve volt lead. The results are displayed with voltage details in a liquid crystal display screen. We also use it to check the MOLEX, SATA, and floppy connectors. These peripheral connectors are only tested using red/green lights. We then dig a bit deeper using a multi-meter to test the 3.3 leads and take a look at the VSB (Voltage Stand By) functionality.

We hope you enjoy. We will be making more videos in the future, so please subscribe.

Thank you!


X6800 says:

Finally brought one of these after all these years. Multi tester is fine, but bothersome.

SgtKilgore406 says:

Would you say this tester is worth the money for getting a basic overview of the power supply ‘s condition? I ask this from the perspective of never testing a PSU (the proper way) and wanting to add PSU testing (in general) to my arsenal. Thanks for the video!

Nick Keith says:

Where did you find the manual for the power supply tester?

Smackerlacker says:


Julia Urbanski says:

What did you print from wikipedia? I’m teaching this to students and I would like to have that printout for them.

HVI says:

This is useless since it can deliver the voltage but some times not the amperage due to leaking capacitors or poor quality. This is a waste of money. You have to take a look in the PSU and see if there are bad capacitors and take a look at the PCB. Some have very small transformers and they are way overrated.

Werner Lieske says:

Fantastic video thanks. I own one as well now. THought I’d have a look at other peoples findings.

Jonasz Przybycień says:

This PSU looks weird. Never saw a transparent one before. Can you tell us whats the model?

Richard Grandbois says:

Awesome thanks. Just received tester with no instructions so your video realy helped.

SirLoneWolf says:

Thanks for the video. As you stated “this Tester comes with no instructions”, so your guide was much appreciated.

CSL says:

Between +12V2 and PG you have 5VSB- Volt Stand By

Mike Dahms says:

I’ve been using one of these for several years now and wanted to share a link to a ‘HOW TO VIDEO” for one of these testers for a friend who has never used one(he lives several states away). Thank you providing a video I am proud to share with him. Job well done. Thank you, Mike

Paul Kelwaski says:

LL  usually means low voltage condition

YoutberUser1212 says:

How can 11.6v power something that needs 12.0v minimum to run properly and still we need to account for efficiency as nothing is 100% efficient where there can be some loss. So if you don’t get 12.1v or 12.2v how will this work properly if you get less than the needed 12.0v?

Paul Kelwaski says:

Great video thanks for sharing … informative

Sir Lord George Edward Reynolds Walinski says:

LL Means Low Level Voltage condition

Владимир Руденко says:

Use correct connector 4p !!!!!!!!!!!!

Dulara Malindu says:

thank you. that helped me.

smilie120 says:

I’ve plugged mine in and the PSU fan won’t start and I just get LL on all the voltages? Assume my PSU is dead?

2verb says:

I ordered one of these and never having used one was at a loss how to navigate the nearly non-existent instructions. (The package contents say a manual is included. They must mean the sad bit of text on the back of the package.) So this video told me everything I needed to know! Thanks!

John c says:

AGPtek Power Supply Tester 12+ L.L mean?

mad mark says:

my pg is 0.0? but it powers things…

WalkerGames says:

i have been having issues with my PC locking up. I will be doing pretty much anything and the screen locks up and I have to do a hard reset. It works perfectly at my friends house but not at mine. I have used two different power supplies but they were pretty low-end ones. Would you recommend getting this device to maybe see what the problem is?

Gina Marsh says:

my tester is flashing L.L and beeping I need to know what to plug into the tester to test this

Menva Fan says:

Or.. Just use a freakin’ multimeter.

Road Runner says:

That constant beeping is triggering me. I’d end up desoldering the internal speaker just to keep it quiet 🙁

Colm Munnelly says:

Eli I have just added you to my hero list. its not a big list!

TheBlarghzorz says:

I just used this an the PG read as zero. Can you shed some insight?

Brando Crispim Vieira says:

I get crashes when stressing the PSU/GPU, is there a way to test it under load with this?

Charles Krautwurst says:

Rule of thumb is within 10% is ok right? so 3.6 should be fine, no?

Jhoel Iván says:

Hola Amigo Tengo ese testeador igual el pg marca 190 pero palpita hace
pitido es normal a que se debe descarte otra fuente normal el
Power Good no palpita nada

Michael Perugini says:

Hope this helps


1. Plug-in 24pin and plug-in (P4 / P6 or P8) connector into the tester before turn on power.
– 20pin ATX PSU: use P4 connector.
– 24pin ATX PSU: use P6 connector.
– EPS PSU: use P8 connector.
2. Turn on your power supply
3. LCD show each voltage and P.G value on the screen automatic and you can hear 2 beep sounds.
4. ATX power output connector checking one by one.
– If power output is working, the LED will light on
– If power output failed, the LED will not light on.
5. Plug-in (HDD/Floppy) connector and check LED light. (+12V1/+5V).
6. Plug-in SATA connector and check LED light (+12V1/+5V/+3.3V).
7. Remove the connector after your checking.
8. DO NOT plug-in 2 connectors in to the tester at the same time. ( Only 24pin and (P4/P6/P8)
9. Abnormal voltage detected will not display on the screen.
10. No voltage detect, “LL” will display on the screen.
11. Detected Voltage lower than Min. value, “LL” will display on the screen.
12. Detected voltage higher than Max. value, “HH” will display on the screen.
13. When detected voltage is lower than table value (A), will alarm.
14. When detected voltage is higher than table value (B), will alarm.
15. P.G value detected lower 100ms or higher 900ms, P>G value is abnormal and alarm.

When abnormal happened, it will alarm and relative digit blink on the screen.

I'm not easy to please If you fall for me says:

hi, where is this cute little device from ?  Is it okay to buy it in China? I see something look exactly the same in China market, I don’t know if that’s the rip off or something

JediNachos says:

Thanks for the info! Good video!

Albert Jansen says:

In your video you say it doesn’t test the 5v SB (purple) but the display shows clearly 5VSB! and the normal 5v together in the display

Daniel's Game Vault says:

I use the exact same tester at work. LL stands for “LOW” and it can also flash HH if that particular voltage goes too high 😉

JouTuber says:

Can i just use SATA hard drive instead of the fan to add load?

arjuna207 says:

why did you short the green and the ground and not test directly? please explain

Adorer Woblin says:

I am using a Coolmax PS tester. All my voltage check out good, however, My PG shows HH. I have tried it on two different PS with the same results. For a quick second it showed 480 on one power supply. My question is what is the PG and what should it read.

Nikolaos Videos says:

Hello, when I press the Power button on the PC it starts for half a second and then turns off. I don’t know if it is a short-circuit or a motherboard problem. I used this PSU Tester on my friends problematic PSU and what happened was, after I powered on the PSU, the tester gave me a blue screen and a wierd sound and after 2 seconds of *charging sound* it turn off completely. Now, it doesn’t show any indications. I hope that the PSU is the problem and I hope that it didn’t fried the psu tester. What do you think?

Frozen Electronics says:

Just wanted to point out, if the voltages are a little high with no load, that’s usually okay (as long as you’re within +/- 10%). If you checked the voltages with a running computer attached I guarantee they’d be spot on (at least for a quality power supply).

MrTVintro says:

I have literally seen this thing with a dozen different brands on it…

Ernesto Epsilon says:

Nice! I got one of these as well but the manual was in chinese.. and or not specific at all. This video explains a lot!

Pyotr Leflegin says:

Useful video. Mine came with no instruction leaflet so this was most welcome. Thank you for sharing your knowledge.

Johnnie C says:

I have been using these for a long time, but never thought to test with the Multimeter duh,, ive probably discarded good powersupplies in doing so,,

Very good video on these, and i now know too to not hook sata , molex and floppy all up at the same time as i have always done 

THANKS this is the most indepth and technical video about this tester !

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