I mean back when Windows came out, there was virtually no "power save" on PCs.
If you mean Windows 3.0, it was for the 286 and there was no power saving that wasn't vendor-specific. For example I have a GRiDPad 1910 and that has a sleep mode. If you mean a recognizable version of Windows NT, it was for the 386 and there was still no standard power saving.
If you wanted to suspend to disk, your BIOS would do that for you.
The OS still had to prepare itself for sleep.
ACPI came out in 1996, well past the prime of Windows.
Yes, but Intel and Microsoft brought out APM in 1992. Their collaboration is a major reason why power management was bad on Linux for years. Microsoft wrote the tools that vendors used to make the tables for power management that went into the BIOS. These tools produced different tables for Windows and for other operating systems. Part of how Linux got to have working power management is that it just started claiming to be Windows, and getting access to working tables.