Noisy Power Supply on FiOS SDTV box

Question

Hello.
Okay, My uncle on Staten Island has FiOS, and has four sets. three HD sets and one older SD set in the basement. When the FiOS service was installed, the TV in the basement had suddenly developed severe amounts of snow caused by RFI from something. Since they had sent him a new SD box, we had connected this in, and got no snow. Okay, get lazy and put the old one back in, and..........still no snow!
Long story short, the problem was the wall-wart power supply sent with the first box was generating severe amounts of RFI that was being picked up by the TV set (an older 70s-80s dial-type set with 300 ohm terminals). We just left the new power supply in place with the original box, and all worked perfectly.
Has anyone else ever had an issue with RFI on older sets from these units?
(PS: Swapping the old PSU back in, even with the new box, brought the massive snowstorm back)
[Can you hear me now? Good!]
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Answer 1

Pobster,
Switching power supplies (such as those used in computers) do not require a "pure" analog sine wave input; they are more than capable of running on PWM/stepped sine wave input. The noise from the power supply when running on power from a PWM output UPS does not indicate that damage is being done to your machine; it's a harmless side effect.
Some equipment will be damaged if powered via PWM input; items with compressors (refrigerators, air conditioners) definitely fall into this category, as well as some medical equipment and telecom equipment.
I live in an area with notoriously dirty power; a UPS is critical in my case (I'd argue that it is critical in any case, however). I've ran my equipment on UPSs for many years, and the price has dropped significantly. I've got one APC SmartUPS with pure sine wave output which was purchased for me by a client, but most of my equipment is running on UPS with PWM output. It's not uncommon for me to have 20-30 power events in a given day - most of them transient voltage drops or spikes; I've still got an old Sun Sparc 10 file server that's still chugging along.
A couple of interesting articles for your perusal:
http://www.macosxhints.com/article.php?story=20051009043816537
http://en.wikipedia.org/wiki/Pulse-width_modulation
A quick google will turn up lots more information on the topic. APC used to have a white paper on their site which talked about this very topic.
Most manufacturers provide connected equipment insurance - tripp lite, for example, provides $250,000(US) coverage. I've never known anyone who actually needed to use this coverage - I certainly haven't .
In brief: A UPS with PWM output will not harm your computer; switching power supplies are more than capable of handling this. If the noise bothers you, look for a UPS with "pure sine wave" output - you will pay more for this feature; it's an aesthetic choice in this case.