I can’t speak for Germany, but I guess that it won’t be much different than Denmark where my experience lies.

Almost all my recommendations has been mentioned before, but I’d like to point out:

• RS in my experience is reliable about 90% of the time. If you put in an order in can arrive in several shipments. I ordered 50 pieces of something got 46 from a UK warehouse and 4 from Germany. That’s another thing, some stuff ships from Frankfurt am Main, so no waiting for imports.
• Reichelt is good for cheap instruments. I’ve never used them for components, I prefer RS for that, but for instruments they carry some of the Chinese stuff that you can’t get other than on ebay or ali.
• Digikey stocks so much electronic components that sometimes you can’t avoid them. Where RS is really fast, their stock and prices are more suited for prototyping than production. Digikey is where you can get the specific series of cap and value you need for your repair project. Digikey will handle all the import and customs stuff as well.
• https://el-supply.com/ is new to the post. They’ve been in business since the 70s, but is primarily targeted towards Denmark. But they do have an international site. Some times they can be extremely cheap compared to RS and Digikey, especially with regards to stuff used for teaching electronics. I’ve been a customer since the late 90s privately, and I’ve placed several orders each year professionally since the early 10s as well. Never been let down.

Conrad electronics?

I would at least check mouser.com

Point it at Europe site and see how you go. I have had good luck with shipping from them to both Europe and Australia with decent time.

Had to batch up my orders to make best use of shipping cost.

Octopart searches other sites like mouser, Newport, digikey, etc. for electronic components like a super search. So I use it often in the US, but give it a look to see if works for Europe. It will also show you price trends and let you build a BOM, etc

If you can wait a couple weeks, AliExpress is going to be the cheapest.

eBay may be a bit more expensive, but it’s often my go-to because you can find everything and usually there are options with short shipping times.

For not too obscure parts, I would look at Reichelt, their prices are surprisingly low (especially if you bundle your orders to save on shipping costs).

Overcharge depends on how you value time and accuracy. I like https://de.rs-online.com/web/ and https://www.digikey.de/en as i prefer brand over price. Too many months wasted waiting for stuff like this from aliexpress only to get a counterfeit/ buggy thing.

The cheapest ones will be from china, be it eBay or AliExpress. When buying via eBay never forget to look at the delivery date, I’ve waited up to months because I didn’t check the date…

Depending on your location you may check your local area. Some cities have small private electronics shop, they’re usually a bit more expensive but a) you get your stuff on hand and b) they can often provide feedback and knowledge and give some tips.

And with some luck you may find some broken thing on Kleinanzeigen, which you can salvage for parts.

Newark I thought has a solid European presence. (Several things I’ve ordered came from an overseas warehouse)

I guess your best bet is Pollin. Other than that aliexpress or eBay.