PSU rocker switch doesn't block residual charge

I'm not sure if something's up with my power supply or not. If I turn off my computer, flick the rocker switch on the back of the PSU to off, and wait a few seconds, and turn the computer on, my case lights and fans come on for half a second before turning off. If I wait a minute or even five minutes instead, the case lights and fans remain inactive, but a couple lights (num lock or whatever) do light up on my keyboard for a moment. This only ever works once -- if I try again, nothing happens. So it seems that some residual charge is being kept after I run the computer, which is used next time I turn it on, rocker switch or not. Is this an issue? The PSU is still within an RMA period.

I'm not sure if this is relevant, but it also seems to me that the PSU emits a soft, constant hum when I put my ear right to it that the PSU in my other computer doesn't -- but it could just be the fan, it's hard to tell. My other PSU doesn't have these rocker switch problems, either.

What do you think? Is this abnormal behavior, and is it worthy of a RMA? Thanks.
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  1. Best answer
    Nope, that is completely normal.

    PSU's are comprised of capacitors which verify that the voltage going to the "rails" or the components in your pc are always the same. Capacitors are similar to a battery, in that they work by storing up energy in a cell, and releasing a set amount. This is mostly to protect against voltage spikes or droops coming from your wall.

    So, even though you have no electricity coming into your PSU, the capacitors are still charged, which is where you get the minor electrical current when you press the power.

    This is further proved by how as time goes on, there is less power remaining when you press the button.

    So, long story short. That is normal operation of a PSU.
  2. Okay, thanks, that sorts it out. Strange that my other computer doesn't do it though.
  3. Best answer selected by jbarcel.
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