12v 1amp plug in power adapter/power supply

[#1]

Is there a way of finding out if any of the surplus power supply/power adapters ( black wall plug thingies) is "linear" or "switching" ? ?  

I can`t see anything on the labels.... would connecting to a multimeter, to the output plug,  show anything ? when plugged into the mains, ....  if so... what am I looking for to identify the type ?

[#2]

Look for the symbols discussed here  https://electronics.stackexchange.com/questions/294292/strange-symbol-on-psu-label

[#3]

@SpendLessTime Thanks for the quick reply.... it seems that it looks like the symbol for a transistor,  but with an L indicating "linear"    and an S indicating "switching"...

Unfortunately, two of mine have no such symbol.... gotta go down the shed now and dig out the box with the rest of them in !

cheers

[#4]

@SpendLessTime   Been down the shed... same again... no "transistor" logo.... however... two of them have LPS on the label,... which... could? ? ? ?  mean   "Linear Power Supply"  ? ? ? ?

The second one, has the big round "suppressor"   ? ?   on the output lead....  as used on laptop power blocks... so maybe that would be best for my usage as, hopefully, it will reduce interference on the power line input of the unit I am making ( small short wave receiver using 2 valves ).

[#5]

The second one is a safer supply to use and handle due to it being a Class II (square within a square) and LPS so has better electrical insulation and Limited Power Supply (the LPS part). LPS means it is less likely to go up in flames as it has stricter limits on voltage and current. https://www.cui.com/blog/overview-of-limited-power-source-lps-requirements

EDIT:

Actually I noticed they are both Class II and LPS but the first doesn't show if the plug is centre positive or negative.

[#6]

The ferrite core in the second one is probably a good idea. It cannot hurt in any case.

[#7]

@shutter

Feel the weight. If it's truly linear it must have a 50 Hz transformer built in. If it's light it will be a switcher as these use a much smaller high frequency transformer. The only linear one I have seen for many years came with a Netgear DG834 router.

The one you have with a ferrite will almost certainly be a switcher.

[#8]

@SpendLessTime & @Baldrick1  Thanks for the input guys.... actually done a bit of a google on that LPS... it stands for "Limited Power Supply".. not LINEAR... something to do with techy stuff on how much it can kill you with ! . (or not ).

As for the weight of the two pictured... they are both very light.. ( about equal in weight ).. despite the first one being thin and the second one being more blocky/square/cubic.

I have some 24v dc output one`s in the shed... but I only need 12v... 1a max...  those are about the same size as the second one, but are much heavier.. so presume they have a "proper" transformer inside,... but they don`t have the transistor like logo on them .

To me, it`s not critical,  however, the guy who puts the kit together did mention that a LINEAR power supply was recommended. or 8 x 1.5v D cells.  so maybe I`ll invest in some cheap one`s from ASDA or Morrisons, next time we are there..

Thanks again for the helpful replies...  much appreciated... as always.

[#9]

Which type is most efficient, though?

I'm betting its the switch mode PSU...

It's very expensive to provide 1 amp from batteries.

[#10]

@VileReynard  I don`t think the "efficiency" is the problem with this little set..... more likely the "smoothness" of the wave produced... which might cause instability in the RF section,... or maybe some noise in the whole circuit, which would degrade the performance.   Not sure how much it draws, but the guy did say that it would need a minimum of 100mA from the mains psu.

The kit includes a holder for 8 AA batteries... so it won`t be drawing a great deal of current.

[#11]

The batteries will be connected in series to give you 12V. Therefore if you need 100mA then each battery must supply the full100mA.  If you look at the battery curves from this link it will show that at this current you will get around 2Ah out of the battery or put another way, 20 hours use. So this could get expensive. It might be worth trying out your power supplies. If you get noise introduced.you could always increase the filtering on the power supply.. Link. https://www.powerstream.com/AA-tests.htm

[#12]

@Baldrick1  Thanks for that information... much appreciate the follow up.... Won`t be using it for extended periods... it`s mainly for a bit of fun... give me something to do... I do have a quantity of rechargable AA batteries, if the need should arise...  taking it at 50% of what you predict... I should think that 10 hours usage would be spread across 6 months or more ! ! ..

Thanks again