If
AidenShaw knew what number was relevant, then he cited that number. Anyone can post a massive color glossy sales brochure .... that does not even define a pure sine wave. He posted no numbers because recommendations only come from what advertising, hearsay, speculation, and subjective reasoning (also called junk science reasoning) has told him to believe.
Well, if one reads all that stuff, then surge protection provided by a UPS is about 230 joules and never more than 460. A surge that miniscule is routinely converted by electronics into rock stable, low DC voltages to safely power semiconductors. UPS does not even do what is already done routinely and better inside electronics.
He only recommends a UPS for 'cleaner' power because propaganda (without any spec numbers) orders us to believe what we are told.
Just as ridiculous is a myth that power is cleaner because is has no gaps. Again, anyone who first learns technology before making recommendations knows that AC power is always electricity with gaps. In fact, computer standards even define how long power can be removed - and internal DC voltages much not vary even by 0.2 volts.
That modified sine wave is not only perfectly good for all electronics. It gets converted into 300 plus volt radio frequency spikes with many gaps. Even that is perfectly ideal power that results in rock stable, low DC voltages. Since it is all done better inside a PSU.
All this stuff, claimed as necessary for a Mac, was already done better inside computers even over 40 years ago. Claims are only subjective because advertising propaganda has created mythical fears.
Even 'interference" was some subjective myth created when basic electrical concepts were never learned. Myths exist when one does not always demand reasons why with numbers. That 'interference' is really 'dirty' electricity output by a UPS when powered from batteries. 'Interference' that quickly degrades near zero joules inside a power strip protector. And in some cases, might cause UPS damage.
So back to what the OP wants. That (dirty) sine wave from most every UPS is perfectly good for all electronics. Second, some disk drives (or its external drive hardware) can be set to sleep when not accessed after a time period. Third, external disk drives, powered by a USB bus, get powered off when that computer powers off. Four, externally powered HDs can be powered from a 'smart' power strip. That cuts off power to other receptacles when the first item (ie computer) stops demanding power.
Unfortunately, a UPS powered from that power strip would not cooperate. But then a UPS is only implemented to provide temporary and 'dirty' power so that unsaved data can be saved. Is it necessary?