I know mine did. I had various machines, including a 233mhz PowerPC tangerine iMac running in a cupboard for a while. They dropped their power bill even lower by switching from a ~150W desktop to a 90W MacBook (which has ridiculously good standby power usage).

It's interesting now, I would have never thought of designing machines (off the shelf bought parts) for low power usage before I moved out.

When I did move out, power was 30 cents per kilowatt-hour and I definitely noticed the difference moving from NVidia to AMD (for a PC that ran 24 hours a day). That PC is now back on NVidia because a single GTX 970 was more efficient than my 2x6870s. I really wish they'd allow me to turn off the dedicated GPU and go back to the Intel iGPU when I'm only running Visual Studio. Lucid Virtu could have done this but it's really buggy.

These days I just make sure Wake On Lan works properly (a challenge in Windows 10 with commodity hardware) and run mostly ARM boxes otherwise.

I don't think I'd even consider running old mainframe equipment in Australia (unless I had 2+KW of solar on the roof)