Try Keemum, that's a proper nice black tea!
I always remember being told that tea has more caffeine than coffee, which is technically true (when unbrewed).
Tea leaves have 3.5% caffeine, whereas coffee beans only have 1-2.2%, but coffee has more extracted, more quickly, by the hot water than tea does.
Coffee is quick release, you get it all in one hit, whereas tea is much slower. It's like the difference between getting glucose from a can of coke, as opposed to long chain carbs that take hours to convert to glucogen.
If you want tea with more caffeine, add more tea to the pot & just leave it to steep for longer.