Yes. SMPS, and UPS are among many that manufacturers do not supply schematics or repair information for. I suspect it is so dangerous to repair these, that it creates that situation. no one wants an injury, or worse, particularly the seller of that product.
Having a schematic in your b/w TV or tube radio manual was not uncommon back in the days. I'm not aware of massgraves of failed DIYers.
And if it's a single voltage simple SMPS, there are actually not a whole lot of parts that can go wrong, schematics are not required to fix it. Other than (quality) components being more expensive than a new one, nothing would have stopped me 
O yes the days when taking the back off an old radio, with the circuit diagram nicely placed on the inside .
Now the manufacturer just use for example caps that have 8000hr working life .. 1 year .just long enough to last passed the garuantee.

then it becomes landfill.
Surely we have to go backwards to pluggable chips again. So the smart TV will be a little bigger. .
Fixing something is very satisfying.
If everyone fixed 1 item . And planted 1 tree
We would be heading into a better world.