For most users with huge consumption increase:

It's because undervolting isn't working for you - You need to set up all in BIOS, find another tool that works or wait for news.

For those with drops to half performance and wierd clocks, it's because mem clock drops from 2xxx to 1000 or core clock drops to 300-900, it's due to high consumption - It's because undervolting isn't working for you - You need to set up on BIOS, find another tool that works or wait for news.

Some cards works with Afterburner Beta 15/16 / Wattool and Claymore (clocks) (especially 4xx) , some don't (mostly 580).

The fix isn't a driver side OC to compensate. If will try ubiq (no dag problem) and ETC (worse than ETH) the hashrate will be the same, the fix is real. Yet some people may experience some consumption increase (not huge - 5%, 10%) or even consumption drop.