WTF is a "computer-rated" capacitor?

High capacitance, low voltage. Computers were somewhat unusual at the time in terms of requiring a lot of current at 5 Volts. The line frequency power supplies were inefficient enough even under optimal circumstances. I've seen some giant transformers from minicomputers of the day. And those huge blue capacitors the size of beer cans.

Apple II was one of the early PC's that used a switching power supply, and it wasn't particularly reliable. I worked at an Apple repair facility, and we replaced a lot of them. But our most common repairs were due to the huge number of chip sockets and low quality gold fingers on the disk controller board edge connector. We were a government agency (county run facility serving a bunch of semi rural school districts) and didn't charge a bench fee. If we could fix it on the spot by just pressing all of the chips back into their sockets, the repair was free and we didn't even log it.

At the time, it was a type of capacitor targeting the specific voltage ranges and tolerances to be useful for a computer.

It's a thing that still shows up in a web search (but is far less meaningful).

The actual term is "computer grade electrolytic capacitor," designed for long-term service in high current linear power supplies. You can still get them, even though few computers use linear supplies these days: https://www.mouser.com/c/passive-components/capacitors/alumi...