Testing DC power supplies for Juniper switches

Just get a meanwell 48v power supply. They are isolated so ground reference doesn't matter. Something like the sdr 480-48. I'd put a fuse inline or get fancy and hook it to a gmt fused distribution panel - search telect gmt on ebay.

There are also some used HP/Agilent models on ebay that look like they would work, but I'd rather get something new if it's not too costly.

Since this is a test bench, I think this is a pretty good option here. The HP/Agilent/Keysight series of system DC power supplies is extremely robust and well made, and I think even a used one is a good choice for this scenario. The 6032A or 6554A would be ideal here, but even used won't be extremely cheap. You'll get accurate controls, accurate meters, if you want you can hook it up to a PC with GPIB and write some automated test routines. The 6554A can also act as a constant-current load (though obviously not at the same time it's powering the supply).

Reasonable quality new test equipment (adjustable, with metering, current limiting and so on) at this power level will be in the $1000-1500 range, and considerably more for a top brand. About the cheapest I'd go for in this category is BK Precision 9111, but at only 180W it's a bit low on the power handling for a good test. The 'right' tool new would be Keysight N5748A, B&K 9115, Aim TTi QPX750SP or a high power bench unit like the R&S NGP800. $1500+ for these.

Other options would be a telecom-style rectifier rack, but the cost of that is likely going to be more than either of the above options, or just buying a closed-frame AC-DC supply in a box with a fuse, input filter, and switch, but I wouldn't really suggest that.

Ghetto approach is to wire 4 12V SLA batteries together (maybe even splurge and buy a used UPS battery rack), and hook them up to a cheap battery charger when you're not using them :p.

Edit: You will of course also want a decent quality multimeter, and maybe some kind of load, to test the output. You can probably skip the load, by measuring the supply's output voltage and making sure it is reasonable, and using a spare switch as a load.

You don’t need the variable supplies like others have been linking

Just get something like this (not suggesting this exact one, just random one I found)

Wire up some appropriate sized wire with spade connectors on both ends and you are good, maybe put something additional over the “spicy” end to keep hands from getting the ac side easily

That and hook the ac side to a power switch so you can kill the Dc output before disconnecting it

https://www.ebay.com/itm/DC-48V-10A-LED-Driver-48-Volt-10-Amp-Transformer-480-Watt-48Vdc-Power-Supply-/184513722903?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=711-127632-2357-0

Edit this is with the assumption you have chassis to plug these into, if you are wanting completely standalone testing that’s a LOT More complicated since you need to measure the outputs as well as understand if there any control logic that the chassis does to tell the PSU to boot up

48 VDC power originated from large lead-acid battery banks. 48 VDC is nominal battery voltage, 52-54 V is what's usually present (lead-acid float charging voltage).

For a cheap go/no-go, I'd get a 48 V golf cart charger, and 4 12V lead acid batteries (even the small ones, like the SLAs used in UPSs), and wire that up.

For correct, I'd watch eBay for a working HP/Agilent/Keysight 6654a, which will do up to 60 V / 9 A (or 6030a or 6032a or 6674a, which provide increasing levels of current). That would let you test across a range of input voltages.

Iota engineering dls48 or dls54. They'll do what you want. Super reliable. You won't need the fancy charge controller.

Voltage meter would be the best way