As I understand it, AC/DC SMPS power supplies and unintentional radiators (anything with a chip clocked at a speed of more than 9 kHz) must be FCC compliant.

I am preparing a device which uses an FCC-compliant switched-mode power supply (SMPS).

The power supply will be powering a vacuum pump and a resitance heater, which to my understanding do not require FCC compliance. I imagine I can claim FCC compliance for my system without further testing as the SMPS is rated as FCC compliant by its manufacturer.

  • 2
    \$\begingroup\$ Since you know the term "unintentional radiator" then you should realize that just because your system is not an intentional radiator and contains an FCC-compliant power supply does not mean it isn't an unintentional radiator. Furthermore, did you read the third section about incidental radiators? Which the rest of your system apparently is? fcc.gov/oet/ea/rfdevice That said, "does not need to be tested" does not mean "compliant". \$\endgroup\$
    – DKNguyen
    Commented Sep 13, 2022 at 1:56
  • \$\begingroup\$ Oh, and possible duplicate of this question? electronics.stackexchange.com/questions/634619/… \$\endgroup\$ Commented Sep 13, 2022 at 2:09
  • 2
    \$\begingroup\$ You can't know your system is compliant. Your system is a possible antenna for the switching frequencies of the supply. Win (or lose) the lottery, your system hits a resonance - FCC fail. Getting it tested isn't super expensive (couple thousand $$$ or thereabouts) Any issues probably can be resolved (in real time, during the test) with a properly selected ferrite on the cables. \$\endgroup\$
    – Kyle B
    Commented Sep 13, 2022 at 3:22

2 Answers 2


[Bypassing the question whether or not you actually need compliance, and what kind of compliance do you need.]

A system isn't automatically compliant if it uses a compliant (FCC, IEC, CE) power supply. To become compliant the system has to be tested and approved. Using a compliant power supply, however, makes the approval easier.

As I understand, AC/DC SMPS power supplies [...] must be FCC compliant.

Check what kind of compliance the power supply has. Some initial information may be in the datasheet. Ask the manufacturer for certificates, and test reports.

  • \$\begingroup\$ Yes, for example, if the product comes with a power supply, it will be used in testing, and it is possible that some part of the testing will only depend on the power supply, and that testing might seem redundant, but other aspects of testing will check the whole system. Furthermore, the test report will indicate the equipment used so if there is a question later you won't be able to ship your product with a cheaper power supply :) \$\endgroup\$
    – crasic
    Commented Sep 12, 2022 at 23:45

If the SMPS is packaged as part of the unit, then it needs to be a tested together as an assembly. Then the whole box gets the marking.

If the SMPS is a separate ‘brick’, then the thing it powers doesn’t require EMI testing if it isn’t a radiating device and wouldn’t need to be marked by itself. But the gizmo doesn’t ‘inherit’ the power supply’s EMI certification even if you test it together, since there’s no guarantee that the field user wouldn’t swap the brick for a non-compliant one.

That said, your unit contains a heater. Depending on the wattage it may need safety certification (e.g. UL or equivalent.) And if the supply voltage exceeds SELV limits, that brings in another certification as well.


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