APC Smart-UPS 1500VA RM: Enough for UniFi + Mac Mini?

A UniFi switch, a UDM SE, and a Mac mini together draw somewhere in the 80–200W range depending on how hard the Mac mini is working and how many PoE devices hang off the switch — and the APC Smart-UPS 1500VA RM (SMT1500RM2U) covers that with room to spare, since its rated capacity is 1000W / 1500VA. The harder question isn’t whether it fits, it’s whether you’re paying for headroom you don’t need, and what actually goes wrong if you buy the wrong waveform instead.

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Here’s the load math, model by model, using each manufacturer’s own published figures:

• UDM SE: 50W maximum, excluding PoE output, per Ubiquiti’s own tech specs page for the device. That’s the router/controller/IDS appliance draw only — it doesn’t include anything you plug into its own PoE ports.
• Switch: varies by model, but check the “Max Power Consumption (excluding PoE output)” line on techspecs.ui.com for yours. A USW-24-PoE Gen2, for example, lists 25W self-consumption with no PoE clients attached. Whatever PoE devices are actually drawing power from it — an access point, a camera — adds directly on top, because that power comes through the same wall input the UPS has to carry.
• Mac mini: Apple’s own power-consumption page puts the M2 model at 7W idle and up to 50W under a CPU-maxed synthetic load (the M2 Pro version tops out at 100W). Day-to-day server or task-runner use sits well below the ceiling most of the time.

Stack those up and a switch-plus-UDM-SE-plus-Mac-mini rack typically runs somewhere between 80W at idle and 150–200W under real load with a PoE device or two attached — call it 10–20% of the Smart-UPS 1500VA RM’s 1000W capacity. That’s not a tight fit; it’s a UPS sized for a much bigger rack than the one being described, which is either exactly what you want (headroom to add a NAS or a second AP later, without buying a second UPS) or more than you need (if this three-device rack is the whole plan, forever).

How long it runs at that load

APC’s published runtime curve for this battery platform is steep: it lists roughly 25.8 minutes at a 500W half-load and drops to about 7.2 minutes at the full 1,000W rating. At the much lighter loads this workload actually produces — closer to 100–150W — the same runtime chart curves up toward the 150–200-minute range, because a lead-acid pack sized for 1000W barely notices a 100W draw. In practice that means enough runtime to let a NUT (Network UPS Tools) or apcupsd shutdown script close down the Mac mini and UDM SE cleanly during any outage that isn’t a multi-hour grid failure, with margin left over. Network UPS Tools lists this UPS family as working with the usbhid-ups and apcsmart drivers over its USB port, which is the standard way homelabbers script an automatic shutdown rather than babysitting a battery alarm.

When the smaller 750VA RM is the better buy

If this three-device workload is genuinely the whole plan — no plans to add a second AP, a camera, or a NAS to the same UPS — the APC Smart-UPS 750VA RM (SMT750RM2U) is a legitimate downgrade, not just a cheaper one. Its 500W / 750VA capacity still covers a 150–200W draw with plenty of margin, it’s the same pure sine wave output, the same 6x NEMA 5-15R outlet count, and even the same 2U rack height, so you save on price and get a shorter runtime, not a smaller footprint. Two things narrow that case: Schneider Electric’s own listing marks the SMT750RM2U as not sold in Colorado, Vermont, or Washington (a state appliance-efficiency restriction, not a stocking issue), and its runtime curve is proportionally thinner — roughly 16 minutes at a 250W half-load versus the 1500VA unit’s 25.8 minutes at 500W — so there’s less cushion if you ever add load without upgrading the UPS. If either of those applies, or if a NAS or second switch is plausible within the UPS’s service life, stick with the 1500VA RM.

Why the CyberPower OR1500LCDRM2U isn’t the swap

CyberPower’s OR1500LCDRM2U looks like a direct, cheaper rival on paper — same 1500VA rating, same rackmount form factor. Its own product page lists two differences that matter here: the output is rated 900W rather than 1000W at that same 1500VA (a lower power factor), and the waveform is listed as simulated sine wave rather than pure sine. That second point is the disqualifying one for this specific workload. Active power-factor-corrected switching supplies — the kind built into modern routers, mini PCs, and gateway appliances, including the UDM SE and the Mac mini’s power brick — are the class of device that runs least predictably on a stepped-approximation waveform: some tolerate it fine, others run less efficiently, buzz audibly, or behave erratically on the transfer to battery. A pure sine wave output, which the Smart-UPS 1500VA RM provides across its full line, removes that variable entirely rather than leaving it to chance per device.

If a rack isn’t fixed

Nothing about the load math above depends on rack mounting specifically — it’s the battery capacity and waveform that matter, not the chassis. APC sells the same 1000W/1500VA pure sine wave platform in a tower case (the Smart-UPS 1500, model SMT1500) for anyone whose switch, UDM SE, and Mac mini live on a shelf rather than in a rack. The load and runtime numbers above carry over unchanged; only the six outlets’ physical orientation and the mounting hardware differ.

What else to budget for

The one recurring cost this UPS category has that a router or switch doesn’t is the battery itself. Schneider Electric rates the APCRBC133 cartridge — the correct replacement for the SMT1500RM2U, SMT1500RM2UTW, SMT1500RMI2U, and SMT1500RMUS — for 3–5 years of expected life, and it’s a hot-swappable, tool-light cartridge rather than a shop repair, so replacing it doesn’t take the rack offline. It’s not a purchase to make alongside the UPS; it’s one to expect a few years in, when the LCD panel or the shutdown software starts flagging a battery self-test failure.