USB Power supply noise reduction question

[Rob Strand]

With only 2A available from most USB style power banks, this means my idea is fundamentally flawed I think.

If your target is the pedal you mentioned earlier it depends how much current it *really* draws from the 15V rail. 

[jimcroisdale]

The manual says 15dc 400mA. It's a high gain valve based design (12AX7) so that explains the power draw. To be honest, whatever I build is trying to compete with a 15v wall wart. My friend is saying that they don't last that long and wants a better solution. I can imagine that absolutely spanking a $1 DC DC boost chip to its limit trying to get enough power out of 5v may not be the most reliable way to achieve what I need (even if I can do it)

BUT, if I move away from 5v then I'm into mains supply which is an area that I have no experience at all in so far.

[Rob Strand]

My friend is saying that they don't last that long and wants a better solution.

The best way to increase reliability of a switch mode is to use one with a higher rating.

You want the power supply to run between 50% and 80% of the label rating. The lower the percentage
the longer the supply with last; but only upto a point as running at 10% might be unwise.   So if you need 400mA then you would buy one with a label rating between I1  = 400 mA / 0.5 = 800mA and   I2 = 400 mA / 0.8  =  500mA

The idea behind this is the PSU runs cooler and that directly affects its lifetime.  Particularly the caps.

There are specifics that change the result like the efficiency of the power supply and the size of the box. As a consumer there's only so much info you can scrape from the info available.  A large box alone could be inefficient and just be big because it has a low switching frequency.   Another factor is toughness against mains spikes and lightning strikes.

I had a switch-mode running my cable modem which operated at 50% of the label and it was running continuously for about 10 years without a problem.  It was still running when I replaced the modem.     It was made by Delta Electronics (Thailand).  I think Mouser and Digikey sell this brand.   The other brand was Elpac [now Inventus Power].  I used 100's of those at 50% to 80% rating and didn't see a failure in 10years  (other than people physically smashing them).    Both of these examples were "desktop" style power adaptors,

https://duckduckgo.com/?q=desktop+power+adaptor&iax=images&ia=images

If you just buy cheap Chinese stuff then I suspect it will fail sooner.   Nonetheless using a derating factor like I explained above might still help it!