I have a rig with one RX 550 4 GB, one HD 7950 3 GB and one R9 290 4 GB. All mine ETC 59 MH/s @ 398 W at the wall (measured with power meter).
Also it's an 850 W PSU, only bronze rated.
RX 550: 11.35 MH/s
HD7950: 24.46 MH/s
R9 290: 23.13 MH/s
I'm trying to buy older AMD cards because they are really cheap and still profitable, if you known how to config them.
Wow. I think something must of changed in the new ETC algo because these figures would of been very difficult to achieve back in 2016.
I had a bunch of the r9 290 and if you undervolted them to the min it still pulled 200 watts while hashing at 25-26mhs. You could give it more juice and get it to hash at 29-31mhs but it consumed way too much power.
The 7950 all pulled at least 200 watts, especially when the DAG was low and it hashed > 20mhs.
Add in your 550 plus the Mobo+cpu+fans i would way over 400 watts.