CyberPower ST900U 900VA/500W Standby UPS Battery Backup — Slim

Reviews

1. N No One You Know 1/5

   Defective unit arrived

   USB ports charge phones but the AC outlets won’t accept plugs — even with a three-prong adapter. The unit beeps every five seconds and didn’t restore power after 8 hours of charging. It’s heavy for its size. Returning for a replacement.

2. S salty dog 5/5

   Does what it should

   Performs exactly as advertised.

3. T Tera C 5/5

   Solid year of trouble-free use

   Owned it for a year and it’s still doing its job with no issues.

4. C Cheryl D. 4/5

   Outlets were stuck out of the box

   When I first unboxed it none of the outlets would accept plugs — they were blocked. Customer support was helpful. They advised powering off, unplugging, then forcing the UPS's own plug into each socket to free them; after that they stayed open. I haven’t tested it through an outage yet but at least the outlets now work.

5. M Mario Beauvais 5/5

   Good unit with 12 outlets and 2 USB ports

   Versatile and performs well with its dozen outlets plus two USB charging ports.

6. C cat lover 5/5

   Handy for powering recliner during outages

   This is the third backup I’ve owned. It gives me enough time to close my electric recliner so I don’t get stuck when power cuts happen.

7. J Jill Parsley 5/5

   Quiet and dependable

   No noticeable noise and excellent day-to-day value. It protects my desktop and laptop and the battery life has met my needs so far. Plenty of outlets and reliable operation.

8. J Jonathan M 5/5

   Saved my gaming PC

   This unit has already protected my gaming PC a few times. It works as expected and is well built. I run my PC, monitor and a PS5 from it at the same time.

9. B Ben07 5/5

   Right size for a small system

   I needed a UPS for a mini-ITX setup where calculated demand was about 270W. Pushing CPU/GPU to 100% I never saw past ~200W, so this 900VA/500W model is a good fit. I also bought extra units to protect other systems rather than risk voltage events.

10. M McGadget 5/5

    Perfect for modem, VoIP and phone backup

    Purchased to keep internet and phone services alive during outages. I tested a home hub, a VoIP box and a cordless phone together — they ran for two hours with capacity left. I disabled the alarm with a double-press, which is quick and convenient. Simple, effective and exactly what I needed.

11. D Dr.Seuss 5/5

    Handled an early outage perfectly

    Bought this to protect a PlayStation 4, plasma TV, streaming box and DVD player. After only a couple hours of charging we had a long storm outage and the UPS let us shut the console down without data loss. Simple to set up, ample outlets and useful high-current USB charging. Good basic performance.

12. H Hobo Roller 5/5

    Great value for the price

    I have this powering my micro-ATX gaming rig, 7.1 home theater, 50" TV and a small slow cooker. The PowerPanel app shows real-time load (roughly 80–180W with everything on) and voltage behavior, which I like. The unit looks clean and feels solid. My only real gripe is the alarm — it’s not loud but gets annoying, so I turned it off and rely on software alerts. Under full use I get around 10–20 minutes of runtime, enough to save work or power down safely.