...if a capacitor datasheet doesn't specify DF or ESR and this (or ripple current, etc.) are important to your application then don't use that capacitor...
I typically buy from Mouser. In almost every case where I've searched for an electrolytic, the DF is given. It's just the ESR/impedance that is not always given. Occasionally both are given, which is very helpful.
Note that while DF and ESR are directly related, DF effectively specifies the inverse Q of a capacitor - that is, the ratio of ESR/Xc - and is often only given at a low frequency, a single temperature and as a worst case value, whereas ESR might be given at a low frequency or 10kHz or 100kHz, or with a chart showing how it varies over frequency and/or a chart showing variation with temperature, and is most often given as an average or typical value. Note, also, that the manufacture might not even check DF via sampled testing, whereas ESR typically will be.
I don't often see data sheets with a nice graph of ESR over a broad range of frequencies. Usually when I actually do get lucky enough to find an electrolytic datasheet with both DF and ESR, the ESR is listed in a table at a single fixed frequency. And sometimes the ESR at that fixed frequency is shown at 20°C or 25°C as well as -10°C.
Here's an example recapping project of vintage hardware. It's a switching power supply made by SONY in late 1980's and is used in an external Apple HD20SC hard disk enclosure. I have no schematic and redrawing the schematic is more trouble that it's worth.
Here are photos. And here is a list of all the electrolytic capacitors in that PSU, followed by the Mouser replacement cap which I selected:
C226: 22uF 35V, D=5.2mm, Leads=5mm -- (Mouser:
UHE1H220MDD1TD)
C202: 47uF 25V, D=5.2mm, Leads=5mm -- (Mouser:
EEU-FR1E470B)
C222: 47uF 25V, D=5.2mm, Leads=5mm -- (same as C202)
C109: 150uF 400V, H=32mm, D=25.8mm, Leads=10mm -- (Mouser:
860021383023)
C110: 4.7uF 350V H=32mm, D=12.8mm, Leads=5mm -- (Mouser:
UPM2G4R7MHD)
C210: 330uF 16V, D=8.1mm, Leads=5mm -- (Mouser:
EEU-FR1E331B)
C215: 470uF 10V, D=8.1mm, Leads=5mm -- (Mouser:
EEU-FR1E471YB)
C213: 22uF 100V, D=10.2mm, Leads=5mm -- (Mouser:
UBT2A220MPD1TD)
C214: 2200uF 10V, D=12.7mm, Leads=5mm -- (Mouser:
UHE1C222MHD1TO)
C209: 2200uF 16V, D=12.7mm, H=30mm, Leads=5mm -- (same as C214)
CR-35 daughter card:
C181: 100uF 10V, D=5.2mm, Hmax=12.5mm, Leads=5mm -- (Mouser:
EEU-FR1E101)
C182: 100uF 10V, D=5.2mm, Hmax=12.5mm, Leads=5mm -- (same as C181)
Clicking on the Mouser links of course take you to the capacitor product page, and you can see specs like DF, Life and so on. But you can also then click on the Datasheet PDF to see more. For example, consider the datasheet of the very first cap --
Panasonic UHE1H220MDD1TD. On the first page you see the DF for this 50V 22uF capacitor is 0.10@20°C. Scrolling down to the page in the same PDF marked "222" we see MAX Impedance is given at 100kHz at both 20°C (0.7Ω) and -10°C (2.8Ω). There is no graph of ESR over a broad range of frequencies, but I consider this kind of datasheet good enough. And although I don't have a schematic, I know the PSU is a switcher, and I believe the capacitor impedance values shown are sufficiently low, yet not too low. In this particular case, all the data sheets are quite informative with 100kHz values for Impedance except the
Wurth cap, but I picked that Wurth cap because it is one of the few long life caps available that is physically sized to fit properly. However, there are other caps, yes even quality Nichicons, which have data sheets lacking in details such as the following:
https://www.mouser.com/datasheet/2/293/e-umv-1512793.pdfI do get DF, but no detailed impedance info.
Here's yet another example of a Nichicon datasheet slim on impedance details:
https://www.mouser.com/datasheet/2/293/e-sv-5439.pdfWhen recapping old boards, physical size of the replacement cap is a key consideration, and sometimes there is maybe only 2 or three choices, and when all the data sheets are slim on details, I need to make the best decision I can based on that limited information. And that is why I posted my opening post, to determine what datasheet spec of an electrolytic cap should usually be given priority when I am trying to find replacements for old existing caps.