Hi there,
considering even a modest PSU is rated 15-18A for the 12V DC rail (and maybe 40A for the 5V DC rail), I wonder why I do not hear more about these being used for exterior lighting? They are mass produced, which means they are cheap to get or to replace. They are fairly reliable and I would say safe (I did not hear about a house fire started by a PSU yet). They have internal cooling and if they overheat, they will shutdown.
As long as it is installed indoors (garage? workshop?) then all looks OK to me. They plug into a power point and the wiring on low voltage is not prescribed work, so you can do whatever you want without needing an electrician. Of course you need to have common sense and use properly sized cables, fuses switching gear and such, but otherwise I do not see a downside?
what do you think?
Secondly, why are not the isolating transformers more often used for garden lights? You can get then lots of power (and light) safely, while using standard fittings and bulbs (cheaper). With an isolating transformer there is no way you can get an electric shock (this is why they were created). You can easily get 1kW or 2kW isolating transformers. Not entirely sure if this requires an electrician (it is mains voltage, but at the same time safe?). This is just an idea... but the PSU thing looks doable!