I tried buying TEL on EtherDelta and had two failed transactions in a row, both charged at the max gas price, one after like 15 mins and the other instantly. How come I get charged for a failed transaction?
It doesn't matter what was the result of your transaction, the computations were made and you have to pay for them.
This is how Ethereum blockchain works, if you send a transaction, some miner will receive it, make computations to execute your transaction. And in any scenario,
success, he made his work and he is getting the reward.
I tried buying TEL on EtherDelta and had two failed transactions in a row
In your scenario you should definetelly contact customer support of Ether Delta.
both charged at the max gas price
This part of your question was already answered here.
Failed transactions send all of the gas available for that transaction (the gas limit) to the miner. It’s kind of a penalty for failed transactions.