Substituting old linear PSU for modern switching?

Thread Starter


Joined Oct 5, 2008
I have an electronic computer server room device which is old and has a failing wall-wart power supply. It appears to be a switching power supply as it is very tiny but the wall wart is rated to provide 9 volts DC @ 1 amp. A voltmeter on a good one of these shows an actual output of about 9.5 volts.

I have a collection of older linear wall-wart power supplies, some of which also say they are rated for 9 volts DC output, but when I measure it with a voltmeter the output is definitely not 9 volts, but anywhere from 12 v to 15 v DC.

If I understand this correctly there is a relationship of volts to amps, and if the linear supply can't provide the amperage then the voltage will drop. So perhaps the 12 to 15 v DC will drop to about 9v when it is required to produce the rated 1 amp.

Is there a potential risk of blowing up a modern device designed for a modern switching power supply, due to the proper switching supply holding the output voltage to a much tighter tolerance than the old style linear DC power supplies?


Joined Mar 14, 2008
A linear supply should be fine but it must be a regulated one, with open-circuit voltage close to the desired.
The ones you have appear to be unregulated.
It's true they likely drop to the design voltage when loaded, but unless you measure the actual load under all conditions and use that load to measure the output voltage, you can't know what the true operating voltage will be.

Just buy a new wallwort.
They're not that expensive.