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What's the risk of using PSU that is underpowered? Is there risk to the device drawing the power?

I have a TPLINK AC1900 Onhub Router. It is missing the PSU (12VDC, 3A)

I have a 12VDC 2A. I think the only risk is that I'll blow the PSU ( I guess it might heat up as well. Perhaps dangerously??). The PSU is a leftover, so I don't mind the risk of blowing it.

But... perhaps there's some risk to the OnHub as well? -Clay

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  • \$\begingroup\$ It might run, and most devices use peak power and some margin to size the supply, but if it ever needs 3A and the power supply can't supply enough voltage, you'll get a latch up in the digital electronics. Probably not worth having to reset it every so often. Just buy one that will source the right power. \$\endgroup\$
    – Voltage Spike ♦
    Commented Jun 15, 2017 at 22:32

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All concern scenarios are possible, including that the combination will work. All depends on details of PSU design and TPLINK and PSU design margins. Consider the following:

  1. PSU might have no problem if it is designed to switch to constant current mode when the load reaches the threshold, with proportional drop in voltage. Or it can turn voltage off, and fall into "max short current" mode. You can research your PSU using variable load (variable resistor, potentiometer) to figure this out.

  2. The TPLINK power consumption (3 A) is likely overstated, with some margin. We don't know what these safe functional margins are.

  3. The PSU capability is likely understated, and with free-air cooling at room temperature it might output some 20-30% more than 2 A. So, overstated consumption with understated limits of PSU might provide working combination under normal room conditions.

  4. If the PSU has the soft voltage cut-off, there might be a possibility of so-called "brown-out" conditions for the TPLINK device. Device protection against the brown-out conditions (exposure to under-voltage transients) requires some special engineering efforts, and might be skipped in quality assurance test program for cheap consumer-grade equipment. So yes, there is some possibility that TplINK hub might suffer from using under-rated PSU. But who knows...

In summary, use your under-rated PSU at your own risk. Or visit your local Goodwill donation center and get a 3-A PSU.

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Yes, you might overwork the PSU, worst case I can imagine is setting it on fire and burning down your house.

Also keep in mind that your router might "brown out"; reset randomly because it does not get the power it needs. So it might not be quite functional, but you can always try. If you are lucky, there is enough design margin on both sides (aka, the PSU is actually capable of more than 2A and the router does not actually need 3A) and it will work fine.

In my point of view, an appropriate PSU is cheap enough that I would not bother with a dodgy solution, but I guess I am boring this way ;)

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