what power supply do i need

[wjwren]

I have a GJD control unit for the outside lights. It doesnt come with a power supply, the manual says either connect it from the 12v supply from an alarm panel or use a "12v dc supply". The spec is 20mA standby and 100 mA in use.

If I buy a 12v supply off ebay which one will be ok without blowing it - or am I safe with 12v and not doing any damage.

Something like one of these, 3watts

https://www.ebay.co.uk/itm/DC12V-Top-Quality-LED-D...

[Silverage]

You’re looking for 4 things when sourcing a power supply, well 5 if you count AC or DC out, but most are DC:

Voltage (has to be an exact match)
Current (in amps - can be higher as it is pulled by the device)
Polarity (most things are centre positive)
Tip size - there are 4 common sizes, endless uncommon ones

[GC8]

5 things - 5: regulated. This means a stable output at the rated voltage, as opposed to a far higher voltage that current draw brings down.

[Mr Pointy]

The 3W version you linked to is 8-11V so not the best one. If you want one from that supplier the 15W 12V is a better option. You'll need to fit it in an encloure & wire it from a fused spur. An easier option is a plug-top PSU like these:

https://www.amazon.co.uk/s?k=plug+power+supply+12v

You'll see a few of them come with adapters to convert the DC plug into a terminal you wire into. It saves cutting the end off & having to find which core is the positive one. You will need a nearby mains socket though.