Recently, a power surge took out a few components in my PC's ATX power supply. While repairing (I hope), one component in the power drew my attention. I'm an electronics engineer, but I'm confused about it's purpose:

enter image description here

At first sight, it looks like a transformer, but with only one connection (the blue cable). Too intrigued, I cut away the tape, and found that the cable was just hooked to the plastic lip. No winding, no other connections.

To make it even more intriguing, the connector goes to the ATX's supply circuit board, but both contacts are on the same trace (i.e. shorted together), just after the mains fuse.

Does anyone know of a legitimate function for this component? I have not been able to find the part number anywhere.

PS: This is not a delayed April 1 prank.

EDIT: Thanks for all the replies and comments below! Later, I found another picture on the 'web, showing an even more sophisticated plastic form to hook the wire loop onto: it even had an anti-falloff feature to avoid to loop from freeing itself.

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    \$\begingroup\$ A weight :D regmedia.co.uk/2011/04/11/fake_1.jpg \$\endgroup\$
    – Eugene Sh.
    May 19, 2017 at 19:35
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    \$\begingroup\$ With the answer you got, I suppose you no longer want to repair the PSU. Throw it away and get a real one :-) \$\endgroup\$
    – Mast
    May 20, 2017 at 9:28
  • \$\begingroup\$ Exactly my thoughts. It's still sitting on the workbench. I installed an older -working- supply for the moment. The 'new' one surprisingly has quite nice connectors, which might be salvable ;-) And a quiet fan! \$\endgroup\$
    – jcoppens
    May 20, 2017 at 14:22

1 Answer 1


It's supposed to look like a passive PFC choke. Real PFC chokes were common in the early-mid 2000s. Those were replaced by active and lighter counterparts on more recent power supplies.

Worst passive PFC knock-off I heard about from my friends in China was that the customers associated heavy weight with PFC chokes, so the manufacturers put a large stone in each non-PFC power supply and marked it with PFC. Then the customers complained that there was a rattle from the power supply to they "improved" quality by wrapping the stone in newspaper to cushion it.

More examples from the interwebz: exhibit A exhibit B exhibit C

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    \$\begingroup\$ Supposed to look like? But it is not? \$\endgroup\$
    – Eugene Sh.
    May 19, 2017 at 19:38
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    \$\begingroup\$ @EugeneSh. With zero turns, no. \$\endgroup\$
    – winny
    May 19, 2017 at 19:41
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    \$\begingroup\$ LOL WOW... juts googled... pretty common practice I see.. And most seem to be stamped PFCxxxx as the part number on top just to give the inspector the nod. \$\endgroup\$
    – Trevor_G
    May 19, 2017 at 19:54
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    \$\begingroup\$ @Trevor I don't think so. Decent PSU manufacturers have QA. It's the PSU manufacturer who is ripping the customer off.. \$\endgroup\$
    – Eugene Sh.
    May 19, 2017 at 20:12
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    \$\begingroup\$ As you can see, the manufacturer of the 'component' might well be the same (compare the photo I included with the one from google). Only it's an improved model: No more taping. The plastic core form has the hook to hang the cable loop from! \$\endgroup\$
    – jcoppens
    May 19, 2017 at 20:30

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