Straight eighth notes are halves of a quarter note. Swing eighths are often notated as
But if you actually play as notated this sounds clunky.
What are the real time values of swing eighths?
In the classic case, the triplet representation is the actual value of swing eight notes in 4/4.The first one in a pair of swing eighths are two eigth note triplets while the second is one eigth note triplet as it's typically notated the following way:
You can also think of it as a quarter note followed by an eigth note in 12/8 as seen below.
There is no "real time value" for swing eights in jazz. It depends on the style of the piece (dixieland has different conventions than John Coltrane tune), on the speed of the tune (you can get almost dotted eighth + sixteenth or even more at slow tempo, and fully straight eighths at high tempo), on the mood of the musicians... Even on a given performance, you can get different values among the musicians, with e.g. the drum player having a heavy triplet feel and the soloist playing quasi straight eighths, which can create interesting tensions.
You may say that on average, you'll get the triplet feel, but there is a whole range around the real 'quarter note + eighth' triplets which is totaly legit. Beginners are advised to start with triplets which makes a notated 4/4 bar a 12/8 bar for convenience. Then as they study, listen, play and build their own style, they diverge from this starting point, and get to understand that the feeling of swing and the importance of phrasing and accentuation.