Power Adaptors, Power Supplies

Improper use of a PS (power supply) often costs money. No joke. It could easily cost you the repair or replacement of the device you are trying to power up, and possibly the PS too.

Manufacturers recommend you use their specified type for this reason and I would advise that you follow that where-ever possible.

Occasions occur though, where the correct PS is not available and a piece of kit is useless because of it. It's not surprising that people are tempted to try others. Indeed, it can work out ok if the compatibility is good.

I'll explain here the key things you need to be aware of when looking at this.


AC or DC

AC Symbol
The symbols DC Symbol


You perhaps already knew they stood for Alternating Current and Direct Current. You don't need to know even that really , but you DO need to know they are different, and one should not be used in place of the other (not entirely true, but best remembered that way).

There is a little potential for some confusion here too, because of the way PS can be named.

The mains input to the PS is always AC, hence some firms might call the whole range of types "AC Adaptors" including those that give a DC output. Some firms will use the term only for those that give an AC output.

Your device will be requiring a relatively low DC or AC voltage, it's important you know which. Mostly they require a PS with a DC output, but AC does occur too. Getting it wrong can destroy your device


Output Voltage (V)

Given in Volts (V), this needs to match as closely as possible what your device specifies. You may find a volt or two either way works too. If a little low, the device may not function correctly, but if it does, I would be happy with that.

If on the high side, it is likely that a little more heat will be produced in the device. This isn't usually a problem , but if the device hasn't been conservatively designed in that regard, it could be. So keep an eye on that if trying it out, and if it seems ok, try it over some hours too (supervised).

Aside from the heating risks, voltages more than a few volts high could destroy your device, quite possibly without any signs of heating beforehand.


Output Current (A, mA)

Given in Amps (A) or milli-Amps (mA). 1 Amp = 1000mA. mA is often used for currents around 1 Amp and below.

This needs to be rated higher than what your device requires. The current rating on a PS is what it could supply at maximum. The device will just draw what it needs. It's better that it isn't running your PS too near maximum for long periods though as the PS will probably heat up.

As a rule of thumb I'll go for a supply that is 1.2 - 1.5 times what the device needs

So if my device needed 800ma (0.8A), I would be looking for a PS with 1 - 1.2A (1000 - 1200mA).



This is only a question with DC.

Getting this wrong is the prime cause of device destruction.

It isn't hard to get it right, once you know about these :

Positive Centre
The symbols Positive Centre


Apart from sometimes being almost illegibly moulded into plastic, symbols can vary a bit in design and orientation. It's important therefore, to look for how the + & - are connected to the centre and outer.

They are both used regularly, so don't try and guess. Look for them on your device and the PS, they must be the same.

General purpose PS often come with sets of interchangeable plugs, and an ability to swap the polarity with a plug and socket or a switch. Look for the symbol there too.