I am trying to increase the level of caffeine in everyday tea to 150mg. I am using powder caffeine with L-theane. The powdered caffeine is obviously very bitter how do I mask the taste without adding fruity style flavours Scott
The average caffeine content of black tea is around 50mg/8oz. Green tea is much lower in caffiene, around 30mg. My guess is that you're trying to replace the caffeine kick of coffee, which is more in the 150mg/8oz range you specify.
So my first suggestion is that you just drink three mugs of very strong brewed black tea, rather than adding powdered caffeine.
If that doesn't satisfy you, the time-tested way to reduce bitterness in tea -- as any Englishperson could tell you -- is to add milk or cream. I see no reason why that wouldn't help cover for the bitterness of powdered caffeine just as well.
You cannot "mask" bitterness, once a flavor is added to food or drink, it stays there. Sometimes people prefer to mix in other flavors which more or less distract them from the bitter taste. You'll know yourself best which flavor works for you, it is dependent on the person. Many of the common examples (like honey) don't work for everybody.
The second thing you can do is to dilute it. Use whatever you want - cream, more water, something with its own (distracting) flavor. Just add enough that the taste becomes pleasant to you.