Check GFI outlets, it's a receptacle with a reset button on it that you can press. They could be in the kitchen, garage, bathroom, basement, or outside. One of the outlets must have tripped and need to be reset unless the GFI went bad.

Outside GFCI outlets are notorious for failing due to moisture problems, even if properly protected by a weatherproof box cover. Since you can protect a whole string of outlets by having them downstream of a single GFCI, the fact that a number of outlets don't work is highly symptomatic of one failed GFCI.

Ours weren’t working and it was the suggestion noted above - needed to reset the GFCI on one of them and then both started working :)

I found the GFCI in garage and reset it. Now the outlets and deck lights are working. It seems the fountain is the culprit. Once i disconnected the plug for fountain, GFCI ia not tripping anymore.
However, out of the 12 deck post lights, only 6 random ones (here ans there, not continuous) are working. Any idea how to troubleshoot that?

Odell Home-

Were all of those lamps working before everything went out? And are the deck post lights low voltage lamps? You could have another GFCI somewhere to deal with, or you simply have some lamps burned out (which you can check by substituting a working bulb for one that is off). If this is a low voltage system, you could have a loose connection in the wiring, or there could be a timer that is off. If you can provide more info, we might be able to make more progress.

The lamps were all working earlier. Im yet to check by replacing the bulbs to see if any have burnt out. The wiring is through the inside of the post and below the deck, that i have no access to.
The ones working fine, do turn on automatically as per the timer.

Out of the 4 posts in the image, only 1 light is working.

That's an awfully small transformer. If six of twelve are now out are you sure that there isn't a second transformer somewhere that you don't know about?

I have no idea... Since all the wiring is on the underside i hardly have any clue how it is all connected and where.

Also, 1 dead light suddenly decided to work tonight.. I am hoping others one would want to join the party too. 😁