I have a small TV which expects 12V DC at 34W. Can I use an adapter with a higher voltage rating (19V for example) as long as it can provide enough amps to satisfy the amount of watts needed by the TV?
If the adapter says 19V, does that mean that it can provide "up to" 19V safely or will it always provide 19V and damage the TV?
No, don't use it! The PSU will supply 19V ("voltage source") and will probably damage the load. There are PSUs that limit output current by dropping/regulating the output voltage (which then can be considered a "current source"), but as long as the required current isn't constant that wouldn't work either. Most devices are designed for a specific operating voltage and sink current respective to their task. E.g. in standby mode your TV will sink a low current, but when the display is on, it will need much more. The power spec "35W" just says, how much power it can provide, but at a higher voltage the load most probably will sink more current. More current at higher voltage means much higher power, which might destroy the load.
